A mixture of 40 litres of milk and water contains 10% water. How much water should be added to this so that water may be 20% in the new mixture?

Let the original fraction be p/q
Now, (120% of p) / (90% of q) = 16 / 21
? 4p / 3q = 16/21
? p / q = (16/21) x (3/4) = 4 / 7

Let original price = Rs. 100
Reduced price = Rs. 75
Increase on Rs. 75 = Rs. 25
Increase on Rs. 100 = (25 x 100)/75 % = 33¹/₃ %

Let income = Rs. 100
Then expenditure = Rs. 75 and saving = Rs. 25
New expenditure = 110% of Rs. 75 = Rs. 165 / 2
New saving = Rs. (120 - 165/2) = Rs. 75/2
Increase in saving = Rs. (75/2 - 25) = Rs. 25/2
? Increase% = (25/2) x (1/25) x 100% = 50%

B's salary is less than A's by (30 x 100)/130 % = 23¹/₁₃%

P = 6q. Thus q is less than p by 5q
? q is less than p by = {(6q - q)/6q} x 100%
= ( 5q/6q) x 100 % = 83¹/_{3 %}

Suppose boys = 3N and girls = 2N
Not adults = (80% of 3N) + (75% of 2N) = (12N/5 + 3N/2) = 39N/10
? Required percentage = (39N/10 / 1/5N) x 100 % = 78%

Let the total number of students be 100
Then, n(A ? B) = n(A) + n(B) - n(A ? B) = (72 + 44 - 100)% = 16%
Now,16% of N = 40
? (16 x N) / 100 = 40
? N = (100 x 40) / 16 = 250

Let side of square = 100 cm
Area = (100 x 100)cm² = 10000 cm²
New area = (130 x 130)cm² = 16900 cm²
Increase in area = (6900 / 10000) x 100% = 69%

Let radius of circle = 100 m
New radius = 101 m
original area = [? x (100)² ]m²
New area = [? x (101)² ]m²
Increase% = [? x {(101)² - (100)²} / { ? x (100)²} ] x 100 %
= 201 / 100% = 2.01%

Let length of square = 100 m and breadth of square = 100 m
Area = (100 x 100) m² = 10000 m²
New length = 130 m and breadth = 120 m

New area of rectangle = (130 x 120) m² = 15600 m²
Increase % = (5600 / 10000) x 100 % = 56%