Q: Equilateral triangle from area — find perimeter: An equilateral triangle has area 3√3 sq cm. Find its perimeter.

Introduction / Context: The area of an equilateral triangle in terms of side a is A = (sqrt(3)/4) * a^2. From area we can get side, then multiply by 3 for perimeter. Given Data / Assumptions: Area A = 3*sqrt(3) sq cm. Concept / Approach: Set (sqrt(3)/4)*a^2 = 3*sqrt(3) and solve for a, then perimeter P = 3a. Step-by-Step Solution: (sqrt(3)/4)*a^2 = 3*sqrt(3)Divide both sides by sqrt(3): a^2 / 4 = 3 ⇒ a^2 = 12 ⇒ a = 2*sqrt(3)Perimeter P = 3a = 6*sqrt(3) cm Verification / Alternative check: Plugging back: (sqrt(3)/4)*12 = 3*sqrt(3) ✓ Why Other Options Are Wrong: They do not align with the derived side length. Common Pitfalls: Misapplying the area formula or taking the square root incorrectly. Final Answer: 6√3 cm

Question 1

Trapezium with sides in ratio — find the smaller parallel side: The area of a trapezium is 384 sq cm. Its parallel sides are in the ratio 3:5, and the perpendicular distance between them is 12 cm. Find the length of the smaller parallel side.

Accepted Answer

Introduction / Context: A trapezium’s area depends on the average of the parallel sides multiplied by the distance between them. Ratios allow us to parameterize side lengths. Given Data / Assumptions: Area = 384 sq cm Parallel sides in ratio 3:5 → let them be 3x and 5x Distance (height) = 12 cm Concept / Approach: Area A = (1/2)*(sum of parallel sides)*height = (1/2)*(3x + 5x)*12 = 48x. Solve 48x = 384, then take the smaller side 3x. Step-by-Step Solution: 48x = 384 ⇒ x = 8Smaller side = 3x = 24 cm Verification / Alternative check: Parallel sides are 24 cm and 40 cm; area = (1/2)*(64)*12 = 384 ✓ Why Other Options Are Wrong: 16 cm and 32 cm mismatch the solved ratio; 40 cm is the larger parallel side. Common Pitfalls: Using the difference of the sides instead of the sum; misreading which side is smaller. Final Answer: 24 cm

Question 2

Trapezium area from two bases and distance: The two parallel sides of a trapezium are 1 m and 2 m. The perpendicular distance between them is 6 m. Find the area of the trapezium.

Accepted Answer

Introduction / Context: This is a direct application of the trapezium area formula using metric units without conversion. Given Data / Assumptions: a = 1 m b = 2 m h = 6 m Concept / Approach: Area = (1/2)*(a + b)*h. Step-by-Step Solution: Area = (1/2)*(1 + 2)*6 = (1/2)*3*6 = 9 sq. meters Verification / Alternative check: Units: meters for lengths, sq. meters for area—consistent. Why Other Options Are Wrong: 18 doubles the correct value; 12 and 6 are incorrect scalings. Common Pitfalls: Forgetting to average the bases (sum then half) or mishandling the 1/2 factor. Final Answer: 9 sq. meters

Question 3

Parallelogram from sides and a diagonal — find area via angle: A parallelogram has adjacent sides 60 m and 40 m, and one diagonal is 80 m. Find its area (in sq m).

Accepted Answer

Introduction / Context: Area of a parallelogram is a*b*sinθ. With a diagonal known, the interior angle θ can be recovered using the law of cosines on the diagonal triangle. Given Data / Assumptions: a = 60 m, b = 40 m One diagonal p = 80 m Law of cosines for diagonal: p^2 = a^2 + b^2 + 2ab*cosθ (for one diagonal) Concept / Approach: Compute cosθ from the diagonal formula, then sinθ = sqrt(1 − cos^2θ), and finally area = a*b*sinθ. Step-by-Step Solution: a^2 + b^2 = 3600 + 1600 = 5200cosθ = (p^2 − a^2 − b^2)/(2ab) = (6400 − 5200)/(2*60*40) = 1200/4800 = 1/4sinθ = sqrt(1 − (1/4)^2) = sqrt(15/16) = sqrt(15)/4Area = 60*40*(sqrt(15)/4) = 600*sqrt(15) sq. m Verification / Alternative check: The other diagonal would correspond to the minus sign in the cosine law; area stays identical for the same θ. Why Other Options Are Wrong: 480 and 320 assume sinθ = 0.2 or smaller; 450√15 is not supported by the cosine-derived angle. Common Pitfalls: Mistaking which diagonal formula sign to use or skipping the sine computation. Final Answer: 600√ 15 sq. m

Question 4

Parallelogram area from sides and included angle: The adjacent sides of a parallelogram are 6 cm and 4 cm, and the included angle is 30°. Find its area.

Accepted Answer

Introduction / Context: The area of a parallelogram equals product of adjacent sides times the sine of the included angle. Given Data / Assumptions: a = 6 cm b = 4 cm θ = 30° with sin 30° = 1/2 Concept / Approach: Area = a * b * sinθ. Step-by-Step Solution: Area = 6 * 4 * (1/2) = 12 cm2 Verification / Alternative check: Units are consistent; the formula directly applies to parallelograms. Why Other Options Are Wrong: 24 and 48 ignore the sine factor or apply it incorrectly. Common Pitfalls: Using cos instead of sin for area or forgetting that 30° has sine 1/2. Final Answer: 12 cm2

Question 5

Parallelogram area via base and corresponding height: One side (base) of a parallelogram is 14 cm, and its perpendicular distance to the opposite side is 16 cm. Find the area.

Accepted Answer

Introduction / Context: Area of a parallelogram equals base times the corresponding height. No angle computation is needed when height is provided. Given Data / Assumptions: Base = 14 cm Height = 16 cm Concept / Approach: Area A = base * height. Step-by-Step Solution: A = 14 * 16 = 224 sq. cm Verification / Alternative check: No other data needed; formula is direct. Why Other Options Are Wrong: 112 halves the product; 210 is unrelated; 56π is circular sector–like and irrelevant. Common Pitfalls: Using slanted side instead of perpendicular height. Final Answer: 224 sq. cm

Question 6

Rhombus with diagonals in 0.8 ratio — area relative to longer diagonal squared: In a rhombus, one diagonal is 80% of the other. The area equals what fraction of the square of the longer diagonal?

Accepted Answer

Introduction / Context: For a rhombus, area = (d1 * d2) / 2. A ratio between diagonals enables expressing the area as a fraction of the longer diagonal squared. Given Data / Assumptions: Let longer diagonal = D Shorter diagonal = 0.8D Concept / Approach: Area A = (D * 0.8D) / 2 = 0.4 * D^2. Thus the area is 2/5 of the square of the longer diagonal. Step-by-Step Solution: A = (D * 0.8D)/2 = 0.4 D^2 = 2/5 * D^2 Verification / Alternative check: Setting D = 10 gives A = 20; scaling D^2 by 2/5 matches. Why Other Options Are Wrong: 4/5 and 3/4 are too large; 1/4 ignores the 0.8 factor. Common Pitfalls: Forgetting the division by 2 in the rhombus area formula. Final Answer: 2/5

Question 7

Rhombus area 144 sq cm, diagonals in 1:2 ratio — find the diagonals: A rhombus has area 144 sq cm. One diagonal is twice the other. Find the lengths of both diagonals.

Accepted Answer

Introduction / Context: Area of a rhombus equals half the product of its diagonals. A given ratio allows solving each diagonal explicitly. Given Data / Assumptions: Area = 144 sq cm Let shorter diagonal = d, longer diagonal = 2d Concept / Approach: Use A = (d * 2d)/2 = d^2. Therefore d = sqrt(144) = 12, so the longer diagonal is 24. Step-by-Step Solution: A = d^2 ⇒ d = 12 cmLonger diagonal = 2d = 24 cm Verification / Alternative check: Check: (12 * 24)/2 = 144 ✓ Why Other Options Are Wrong: 24, 48 doubles area; options with √2 are for squares via side relations, not diagonal ratio given here; 6, 12 halves the correct values. Common Pitfalls: Taking the square root incorrectly or mixing which diagonal is longer. Final Answer: 12 cm, 24 cm

Question 8

Triangle inequality test — pick the set that cannot form a triangle: The lengths (in cm) of three line segments are given. Which set cannot be the sides of a triangle?

Accepted Answer

Introduction / Context: Triangle inequality demands that the sum of any two sides be strictly greater than the third for all three comparisons. Given Data / Assumptions: We check each option against the triangle inequality. Concept / Approach: For each triplet (a, b, c), verify: a + b > c, b + c > a, and c + a > b. Equality is insufficient. Step-by-Step Solution: (2,3,4): 2+3=5>4 ✓(2,3,5): 2+3=5 = 5 → not strictly greater ✗(2,4,5): sums all strictly greater ✓(3,4,5): classic Pythagorean triple ✓ Verification / Alternative check: Only option (2,3,5) fails strict inequality once; hence it cannot form a triangle. Why Other Options Are Wrong: They satisfy all strict inequalities. Common Pitfalls: Accepting equality; triangles require strict inequality. Final Answer: 2, 3, 5

Question 9

Triangle with sides 15, 25, and x — valid range of x: The three sides of a triangle are 15, 25, and x (in units). Which inequality correctly describes x?

Accepted Answer

Introduction / Context: Using triangle inequality, the unknown side must be strictly less than the sum of the other two and strictly greater than their difference. Given Data / Assumptions: Known sides are 15 and 25; unknown is x. Concept / Approach: For sides a, b, x: |a − b| < x < a + b. Substitute a = 15, b = 25. Step-by-Step Solution: Lower bound: |25 − 15| = 10 → x > 10Upper bound: 25 + 15 = 40 → x < 40Range: 10 < x < 40 Verification / Alternative check: Any endpoint 10 or 40 would make a degenerate triangle (not allowed). Why Other Options Are Wrong: They include equality or misplace inequality directions. Common Pitfalls: Allowing equality at the bounds; strict inequalities are required. Final Answer: 10< x < 40

Question 10

Equilateral triangle from area — find perimeter: An equilateral triangle has area 3√3 sq cm. Find its perimeter.

Accepted Answer

Introduction / Context: The area of an equilateral triangle in terms of side a is A = (sqrt(3)/4) * a^2. From area we can get side, then multiply by 3 for perimeter. Given Data / Assumptions: Area A = 3*sqrt(3) sq cm. Concept / Approach: Set (sqrt(3)/4)*a^2 = 3*sqrt(3) and solve for a, then perimeter P = 3a. Step-by-Step Solution: (sqrt(3)/4)*a^2 = 3*sqrt(3)Divide both sides by sqrt(3): a^2 / 4 = 3 ⇒ a^2 = 12 ⇒ a = 2*sqrt(3)Perimeter P = 3a = 6*sqrt(3) cm Verification / Alternative check: Plugging back: (sqrt(3)/4)*12 = 3*sqrt(3) ✓ Why Other Options Are Wrong: They do not align with the derived side length. Common Pitfalls: Misapplying the area formula or taking the square root incorrectly. Final Answer: 6√3 cm

Question 11

Triangle sides in fractional ratio — find the smallest side from perimeter: The sides of a triangle are in the ratio 1/3 : 1/4 : 1/5 and its perimeter is 94 cm. Find the length of the smallest side.

Accepted Answer

Introduction / Context: Ratios can be fractional; you can scale them by a common factor to obtain actual sides. The perimeter ties down the scale. Given Data / Assumptions: Side ratios: 1/3 : 1/4 : 1/5; Perimeter = 94 cm. Concept / Approach: Let the sides be k/3, k/4, k/5. Then sum = k*(1/3 + 1/4 + 1/5) = k*(47/60). Set this equal to 94 to solve k, then select the smallest side. Step-by-Step Solution: k*(47/60) = 94 ⇒ k = 94*60/47 = 120Sides: 120/3 = 40, 120/4 = 30, 120/5 = 24Smallest side = 24 cm Verification / Alternative check: Sum 40 + 30 + 24 = 94 ✓ and the ratio reduces back to 1/3 : 1/4 : 1/5 when scaled by 120. Why Other Options Are Wrong: They do not match the computed side lengths from the ratio and perimeter. Common Pitfalls: Inverting the fractional ratios or using 1:3:4:5 erroneously. Final Answer: 24 cm

Question 12

Equilateral triangle perimeter 90 cm — find area: An equilateral triangle has perimeter 90 cm. Find its area (in sq cm).

Accepted Answer

Introduction / Context: For equilateral triangles, perimeter directly gives the side, and area follows from the standard formula in one step. Given Data / Assumptions: Perimeter = 90 cm → side a = 90/3 = 30 cm. Concept / Approach: Area A = (sqrt(3)/4) * a^2 = (sqrt(3)/4) * 30^2. Step-by-Step Solution: A = (sqrt(3)/4) * 900 = 225*sqrt(3) sq cm Verification / Alternative check: Units consistent; formula is standard for equilateral triangles. Why Other Options Are Wrong: They stem from mis-squaring the side or misapplying the 1/4 factor. Common Pitfalls: Using 30*sqrt(3) instead of (sqrt(3)/4)*900. Final Answer: 225√3 sq cm

Question 13

Equilateral triangle area given — find side length: The area of an equilateral triangle is (√243)/4 sq cm. Find the side length (in cm).

Accepted Answer

Introduction / Context: Area of an equilateral triangle is (sqrt(3)/4)*a^2. Here the area is expressed as (sqrt(243))/4. Recognize that sqrt(243) = 9*sqrt(3) to simplify. Given Data / Assumptions: A = (sqrt(243))/4 = (9*sqrt(3))/4 sq cm. Concept / Approach: Set (sqrt(3)/4)*a^2 = (9*sqrt(3))/4. Cancel sqrt(3)/4 on both sides to get a^2 = 9. Step-by-Step Solution: (sqrt(3)/4)*a^2 = (9*sqrt(3))/4a^2 = 9 ⇒ a = 3 cm Verification / Alternative check: Plug back: (sqrt(3)/4)*9 = (9*sqrt(3))/4 ✓. Why Other Options Are Wrong: 3√3 cm and √3 cm are misinterpretations; 9 cm corresponds to a^2, not a. Common Pitfalls: Not simplifying sqrt(243) or forgetting to take the principal square root. Final Answer: 3 cm

Question 14

Square diagonal scaling with doubled area: The diagonal of a square is 4√2 cm. Find the diagonal of another square whose area is double the first square’s area.

Accepted Answer

Introduction / Context: For squares, diagonal d relates to side s by d = s*sqrt(2), and area A = s^2. Doubling area scales the side by sqrt(2), which in turn scales the diagonal accordingly. Given Data / Assumptions: d1 = 4*sqrt(2) cm → s1 = d1 / sqrt(2) = 4 cm A1 = s1^2 = 16 sq cm A2 = 2*A1 = 32 sq cm Concept / Approach: If area doubles, side multiplies by sqrt(2): s2 = s1*sqrt(2). Then diagonal d2 = s2*sqrt(2) = s1*2. Step-by-Step Solution: s2 = sqrt(32) = 4*sqrt(2)d2 = s2*sqrt(2) = 4*sqrt(2)*sqrt(2) = 8 cm Verification / Alternative check: Diagonal scales by the same factor as side (sqrt(2)); from 4*sqrt(2) to 8 matches scaling by sqrt(2). Why Other Options Are Wrong: 8√2 cm corresponds to quadrupling area; 4√2 cm is original; 6 cm is arbitrary. Common Pitfalls: Confusing diagonal scaling with area scaling; remember area scales with side squared. Final Answer: 8 cm

Question 15

Squares — Diagonal Ratio to Area Ratio: The diagonals of two squares are in the ratio 3 : 2. Find the ratio of their areas (larger : smaller).

Accepted Answer

Introduction / Context: For squares, the diagonal is proportional to the side and area scales with the square of any linear dimension. This item checks proportional reasoning by connecting a diagonal ratio directly to an area ratio without computing actual side lengths. Given Data / Assumptions: Two squares with diagonal ratio d1 : d2 = 3 : 2 Square properties: d = s * √2; area A = s^2 = d^2 / 2 We need the ratio of areas (larger : smaller) Concept / Approach: Because A ∝ d^2 for squares, the ratio of areas equals the square of the ratio of diagonals. No numeric side computation is necessary; simply square each term in the diagonal ratio and simplify the fraction to obtain the area ratio. Step-by-Step Solution: Given d1 : d2 = 3 : 2.Since A ∝ d^2, A1 : A2 = d1^2 : d2^2 = 3^2 : 2^2 = 9 : 4.The larger-to-smaller area ratio is 9 : 4. Verification / Alternative check: Pick d2 = 2 ⇒ d1 = 3. Then A2 = 2^2/2 = 2; A1 = 3^2/2 = 4.5 ⇒ ratio 4.5 : 2 = 9 : 4. Why Other Options Are Wrong: 9 : 2, 9 : 5, 9 : 7 do not arise from squaring 3 : 2. 4 : 3 inverts the order (smaller : larger). Common Pitfalls: Using 3 : 2 directly for area instead of squaring. Swapping larger and smaller by mistake. Final Answer: 9 : 4.

Question 16

Square — Side Increased by 25%: If the side of a square is increased by 25%, by what percent does the area increase?

Accepted Answer

Introduction / Context: Area scales with the square of a linear dimension. When a square’s side increases by a percentage, the area increases by the square of the scale factor minus 100%. This item tests quick percent-compounding intuition without algebraic complexity. Given Data / Assumptions: Original side = s; new side = 1.25s Area formula: A = s^2; new area A' = (1.25s)^2 Percent increase = ((A' − A)/A) * 100% Concept / Approach: If a linear dimension scales by k, area scales by k^2. Here k = 1.25. Compute k^2 and convert to a percentage increase relative to the original area. Keep decimals exact to avoid rounding slips. Step-by-Step Solution: Scale factor k = 1.25.Area factor = k^2 = 1.25^2 = 1.5625.Increase% = (1.5625 − 1) * 100% = 0.5625 * 100% = 56.25%. Verification / Alternative check: Let s = 100 ⇒ A = 10000. New side = 125 ⇒ A' = 15625 ⇒ increase = 5625 ⇒ 56.25%. Why Other Options Are Wrong: 125% confuses scale factor with increase. 50% and 53.75% underestimate the quadratic effect. 62.5% overestimates (mixing 1.25 and 1.5). Common Pitfalls: Treating area as linear and adding 25% only once. Final Answer: 56.25%.

Question 17

Squares — Perimeter Comparison to Area Factor: The perimeters of two squares are 12 cm and 24 cm. The area of the larger square is how many times the area of the smaller square?

Accepted Answer

Introduction / Context: Square perimeter is proportional to side length, and area scales with the square of side length. Doubling the perimeter doubles the side; the area therefore quadruples. This item reinforces the linear–quadratic linkage between perimeter and area. Given Data / Assumptions: P1 = 12 cm, P2 = 24 cm Perimeter P = 4s ⇒ s = P/4 Area A = s^2 Concept / Approach: Compute sides from perimeters, then compare areas. Because s2/s1 equals P2/P1, area ratio equals (P2/P1)^2. Here P2/P1 = 2, so area ratio = 4 : 1 (larger : smaller). Step-by-Step Solution: s1 = 12/4 = 3 cm; A1 = 9 cm^2.s2 = 24/4 = 6 cm; A2 = 36 cm^2.A2/A1 = 36/9 = 4. Verification / Alternative check: Using ratio method: (P2/P1)^2 = (24/12)^2 = 2^2 = 4. Why Other Options Are Wrong: 2 or 3 times ignores quadratic scaling. 5 or 6 times overestimates the effect. Common Pitfalls: Mistaking a linear doubling for an area doubling. Final Answer: 4 times.

Question 18

Square Field — From Cultivation Cost to Fence Cost: The cost of cultivating a square field at ₹135 per hectare is ₹1215. Find the cost of fencing it at ₹0.75 per metre.

Accepted Answer

Introduction / Context: This problem connects unit-rate costing with geometry. We infer the area from cultivation cost per hectare, convert hectares to square metres, get the side length of the square, compute perimeter, and finally compute fencing cost per metre. Given Data / Assumptions: Cultivation rate = ₹135 per hectare Total cultivation cost = ₹1215 1 hectare = 10000 m^2 Fencing rate = ₹0.75 per metre Concept / Approach: Area (hectares) = total cost / rate. Convert to m^2. For a square, side = √area; perimeter = 4 * side. Multiply perimeter by fencing rate to get the required cost. Keep units consistent throughout conversions. Step-by-Step Solution: Area = 1215 / 135 = 9 hectares.In m^2: 9 * 10000 = 90000 m^2.Side = √90000 = 300 m.Perimeter = 4 * 300 = 1200 m.Fencing cost = 1200 * 0.75 = ₹900. Verification / Alternative check: Back-check: Cultivation area 9 ha is consistent with the given costs (9 * 135 = 1215). Why Other Options Are Wrong: ₹360, ₹810, ₹675 underestimate perimeter or misuse units. ₹1800 doubles the correct value (likely treating rate as ₹1.5/m). Common Pitfalls: Forgetting the hectare-to-m^2 conversion (10000). Confusing area with perimeter when applying the fencing rate. Final Answer: ₹ 900.

Question 19

Rhombus — Area from Diagonals: The diagonals of a rhombus are 1 m and 1.5 m. Find the area of the rhombus (in m^2).

Accepted Answer

Introduction / Context: A rhombus has perpendicular diagonals that bisect each other. Its area equals half the product of its diagonals. This problem emphasizes remembering and applying the rhombus area formula with consistent units (metres). Given Data / Assumptions: d1 = 1 m d2 = 1.5 m Area A = (d1 * d2) / 2 Concept / Approach: Use the direct formula for a rhombus area. No side or angle calculations are needed because the diagonals encapsulate the necessary geometry for area computation. Step-by-Step Solution: A = (1 * 1.5) / 2 = 1.5 / 2 = 0.75 m^2.Hence, the required area is 0.75 m^2. Verification / Alternative check: Dimensional check: Product of metres times metres gives m^2, then dividing by 2 preserves units. Why Other Options Are Wrong: 1.5 m^2 duplicates d1*d2 without halving. 0.375 m^2 halves twice (overcorrection). 0.9 m^2 is an unsupported estimate. Common Pitfalls: Forgetting the division by 2 in the rhombus formula. Final Answer: 0.75 m2.

Question 20

Rhombus — Perimeter from Diagonals: If the diagonals of a rhombus are 4.8 cm and 1.4 cm, find the perimeter of the rhombus (in cm).

Accepted Answer

Introduction / Context: In a rhombus, diagonals are perpendicular bisectors. Each side equals the hypotenuse of a right triangle with legs equal to half the diagonals. Once one side is known, the perimeter is four times the side length. Given Data / Assumptions: d1 = 4.8 cm ⇒ d1/2 = 2.4 cm d2 = 1.4 cm ⇒ d2/2 = 0.7 cm Side s = √[(d1/2)^2 + (d2/2)^2] Perimeter P = 4s Concept / Approach: Apply the Pythagorean theorem to the half-diagonals right triangle to compute the rhombus side, then multiply by 4 for the perimeter. Keep decimals precise to avoid rounding errors. Step-by-Step Solution: s = √(2.4^2 + 0.7^2) = √(5.76 + 0.49) = √6.25 = 2.5 cm.Perimeter P = 4 * 2.5 = 10 cm. Verification / Alternative check: A rhombus with equal sides and perpendicular diagonals is consistent: s computed from halves returns an integer perimeter 10 cm. Why Other Options Are Wrong: 5 cm equals the side, not the perimeter/2. 12 cm and 20 cm overestimate s. 8 cm underestimates P. Common Pitfalls: Using full diagonals instead of halves within Pythagoras. Final Answer: 10 cm.

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