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- Question
- A river is flowing with a steady speed of 4 km/h. One rows his boat downstream in the river and then returns by rowing upstream in the same river. When he returns to the starting points, the total distance covered by him is 42 km. If the return journey takes 2 h more than his outward journey, then the speed of his rowing in still water must be?
Options- A. 12 km/h
- B. 10 km/h
- C. 9 km/h
- D. 8 km/h
- Correct Answer
- 10 km/h
ExplanationLet the speed of rowing in still water be u km/h.
Distance in downstream motion = 21 km
and speed downstream = (u + 4) km/h
? Time taken = 21/ (u + 4)
Distance upstream motion = 21 km and speed upstream = (u +4) km
? Time taken = 21/(u - 4)
According to the question.
21/(u + 4) + 2 = 21/(u - 4)
? (21 + 2u + 8)/u + 4 = 21/(u - 4)
? (2u + 29)/(u + 4) = 21/(u - 4)
? (u - 4) (2u + 29) = 21(u + 4)
? 2u2 - 8u + 29u - 116 = 21u + 84
? 2u2 + 21u - 116 = 21u + 84
? 2u2 = 84 + 116
? u2 = 200/2
? u2 = 100
? u = 10 km/h
- 1. Diagonals of a rhombus area 1 m and 1.5 m in lengths. The area of the rhombus is
Options- A. 0.75 m2
- B. 1.5 m2
- C. 1.5 m2
- D. 0.375 m2 Discuss
- 2. In how many ways, the letters of the word 'STRESS' can be arranged?
Options- A. 360
- B. 240
- C. 720
- D. 120 Discuss
- 3. If there number are 2a, 5a, and 7a, what will be their LCM?
Options- A. 70a
- B. 65a
- C. 75a
- D. 70a3 Discuss
- 4. H.C.F of three numbers is 12. If they be in the ratio 1: 2: 3, the numbers are?
Options- A. 12, 24, 36
- B. 10, 20, 30
- C. 5, 10, 15
- D. 4, 8, 12 Discuss
- 5. The banker's discount on a sum of money for 1½ years is Rs. 558 and the true discount on the same sum for 2 years is Rs. 600. The rate percent is:
Options- A. 10%
- B. 13%
- C. 12%
- D. 15% Discuss
- 6. A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8 g/cm3, then the weight of the pipe is:
Options- A. 3.6 kg
- B. 3.696 kg
- C. 36 kg
- D. 36.9 kg Discuss
- 7. If one rolls a fair sides die twice, what is the probability that the die will land on the same number on both the occasions?
Options- A. 1/12
- B. 1/6
- C. 1/24
- D. 1/8 Discuss
- 8. If a = 0.1039, then the value of √4a2 - 4a + 1 + 3a is:
Options- A. 0.1039
- B. 0.2078
- C. 1.1039
- D. 2.1039 Discuss
- 9. (.125 + .027) / (.5 x .5 - 1.5 + .09) =?
Options- A. .08
- B. 1
- C. .2
- D. .8 Discuss
- 10. The speed of a boat downstream is 15 km/hr and the speed of the stream is 1.5 km/hr. The speed of the boat upstream?
Options- A. 13.5 km/hr
- B. 16.5 km/hr
- C. 12 km/hr
- D. 8.25 km/hr Discuss
More questions
Correct Answer: 0.75 m2
Explanation:
Area of rhombus =(d1 x d2)/2
=(1 x 1.5)/2 m2
= 0.75 m2
Correct Answer: 120
Explanation:
Required number of arrangements = 6 ! / 3 ! [? S has come thrice ]
= [ 6 x 5 x 4 x 3! ] /3 !
= 120
Correct Answer: 70a
Explanation:
Required LCM = a x 2 x 5 x 7 = 70a
Correct Answer: 12, 24, 36
Explanation:
Straight forward answer 12, 24, 36
Correct Answer: 12%
Explanation:
| B.D. for 3⁄2 years | = Rs. 558. | |||||||
| B.D. for 2 years |
|
|||||||
| = Rs. 744 |
T.D. for 2 years = Rs. 600.
| ∴ Sum = | B.D. x T.D. | = Rs. | ❨ | 744 x 600 | ❩ | = Rs. 3100. |
| B.D. - T.D | 144 |
Thus, Rs. 744 is S.I. on Rs. 3100 for 2 years.
| ∴ Rate = | ❨ | 100 x 744 | ❩% | = 12% |
| 3100 x 2 |
Correct Answer: 3.696 kg
Explanation:
External radius = 4 cm,
Internal radius = 3 cm.
| Volume of iron |
|
||||||
|
|||||||
| = 462 cm3. |
∴ Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.
Correct Answer: 1/6
Explanation:
Let E = Event of getting same number on both the occasions
= (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)
? n(E) = 6
? Required probability = 6/62 = 1/6
Correct Answer: 1.1039
Explanation:
= √(1 - 2a)2 + 3a
= (1 - 2a) + 3a
= (1 + a)
= (1 + 0.1039)
= 1.1039
Correct Answer: .8
Explanation:
Given expression
= [(0.5)3 + (0.3)3] / [(0.5)2 - 0.5 x 0.3 + (0.3)2]
= [a3 + b3] / [a2 - ab + b2]
= [(a + b)(a2 - ab + b2)] / [a2 -ab + b2]
= a+b
= 0.5 + 0.3
= 0.8
Correct Answer: 12 km/hr
Explanation:
Speed of boat in still water = 15 - 1.5 = 13.5 km/hr
Speed of boat in upstream = 13.5 - 1.5 = 12 km/hr
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