Ratio and Proportion – Quantitative Aptitude -02

(01) How many sides does a regular polygon have whose interior and exterior angles are in the ratio 2:1?

Each exterior angle of polygon = 360/n

Each interior angle of polygon = ( n – 2 ) × 180 / n

Thus, ( n – 2 ) × 180 / n : 360/n = 2:1

Thus, n = 6

The regular polygon has 6 sides



(02) The ratio of present age of two brothers is 1:2 and 5 years back the ratio was 1:3. What will be the ratio of their age after 5 years?


Present ages of brothers –> x and 2x

5 Years back the ratio was 1 : 3
x – 5 / 2x – 5 = 1 / 3

x = 10

Present ages of brothers – 10 and 20 years,
After 5 years their ages = 15 years and 25 years

Required ratio = 15 : 25 = 3 : 5



(03) The product of two positive integers is 1575 and their ratio is 9 : 7. The smaller integer is

First integer = 9x and Second integer = 7x

9x × 7x = 1575

x² = 25, x = 5

Smaller integer => 7x = 7 × 5 = 35

Hence smaller integer is 35



(04) The students in three classes are in the ratio 2 : 3 : 5. If 40 students are increased in each class, the ratio changes to 4 : 5 : 7. Originally, the total number of students was

Original Ratio = 2 : 3 : 5
New Ratio = 4 : 5: 7 (when 40 students increased)

Difference in ratio in each class = 2x
This difference arise due to increase in 40 students
Hence, 2x = 40,
==> x = 20

So, number of students in each class = 2(20), 3(20) and 5(20) = 40, 60 and 100

Total number = 40 + 60 + 100 = 200



(05) The ratio of copper and zinc in brass is 13 : 7. How much zinc will be there in 100 kg of brass?

Required quantity of zinc => (7/ 13+7) * 100
=>( 7 / 20 ) × 100
=> 35 kg

Hence 35 kg of zinc will be there in 100 kg of brass



(06) A and B have monthly incomes in the ratio 5 : 6 and monthly expenditures in the ratio 3 : 4. If they save Rs. 1800 and Rs. 1600 respectively, find the monthly income of B

Sol:
Monthly income of A and B be 5x and 6x

Monthly expenditures of A and B be 3y and 4y

5x – 3y = 1800 and 6x – 4y = 1600

Solving above equations; x = 1200 , y = 1400

Income of B = 6x = 6 (1200) = Rs. 7200


(07) Divide Rs. 7500 among A, B and C such that A’s share to B’s share is in the ratio 5 : 2 and B’s share to C’s share is in the ratio 7 : 13. How much will B receive?

A : B = 5 : 2
and B : C = 7 : 13,


thus A : B : C = 35 : 14 : 26

Thus, B’s share = 14 / 75 × 7500 = Rs. 1400



(08) Three numbers are in the ratio of 3 : 2 : 5 and the sum of their squares is 1862. The smallest of these numbers is:

Numbers are 3x, 2x and 5x

Sum of their squares is 1862
(3x)² + (2x)² + (5x)² = 1862

38x² = 1862

x = 7

Smallest number = 2x = 2 (7) = 14



(09) The sum of three numbers is 98. If the ratio of the first to the second is 2 : 3 and that of the second to the third is 5 : 8, then the second number is:

Let the numbers be x. y and z, thus x : y = 2 : 3 and y : z = 5 : 8

Thus, x : y : z = 10 : 15 : 24

y = 15 / 49 × 98 = 30

Hence the second number is 30



(10) A mixture of 30 liters contains milk and water in the ratio of 7 : 3. How much water should be added to it so that the ratio of milk and water become 3 : 7?

Quantity of milk = 7/10 × 30 = 21 liters, quantity of water = 3/10 × 30 = 9 liters

Let x liters of water should be added

21 / 9 + x = 3 / 7

x = 40 liters

Hence 40 liters of water should be added to make milk to water ratio 3:7

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