Question

The ratio of number of boys and girls in a class of 20 students is 1 : 4. How many boys should join so that ratio becomes 1 : 2.  
1. 2
2. 5
3. 6
4. 4

Answer 1

Correct Answer - Option 4 : 4

Let the two number of boys and girls be B and G

Given:

The ratio of number of boys and girls in a class of 20 students is 1 : 4.

⇒ B : G = 1 : 4

Calculation:

Since, The ratio of number of boys and girls in a class of 20 students is 1 : 4.

⇒ B : G = 1 : 4 and B + G = 20

⇒ x + 4x = 5x = 20

⇒ x = 4

⇒ Number of boys = 4 and Number of girls = 4x = 16

To make ratio B : G = 1 : 2 where number of girls = 16

⇒ 2y = 16

⇒ y = 8

⇒ Number of boys required = 8

Earlier, Number of boys = 4

∴ Number of boys that should join so that ratio becomes 1 : 2 = 8 – 4 = 4