Hello! It can be solved with proportional knowledge. Because the number of boys is 30% less than that of girls, the ratio of boys to girls is (1-30%).

): 1 = 7: 10, and now the ratio of boys to girls is 75%: 1 = 3: 4.

Solution: Let the original number of boys be 7x and the number of girls be 10x.

(7x+2):( 10x-4)=3:4

3( 10x-4)

=4(7x+2)

30x- 12=28x+8

30x-28x=8+ 12

2x=20

x= 10

So the result is 7x 10=70 for boys and 0x10 =100 for girls.