Question

there are 600 pupils in a school. the ratio of boys to girls in this school is 3:5.How many girls and how many boys are in the school

Answer 1

In order to obtain a ratio of boys to girls equal to 3:5, the number of boys has to be written as 3 x and the number of girls as 5 x where x is a common factor to the number of girls and the number of boys. The total number of boys and girls is 600. Hence 

3x + 5x = 600 

Solve for x 

8x = 600 

x = 75 

Number of boys 

3x = 3 × 75 = 225 

Number of girls 

5x = 5 × 75 = 375

Answer 2

$3x+5x=600\\ 8x=600\\ x=75\\\\ 3x=3\cdot75=225\leftarrow \text{boys}\\ 5x=5\cdot75=375\leftarrow \text{girls}$