Quick i need answer

Question

In a school of 600 students,the number of boys is 40 more than the number of girls.3/4 of boys and 5/7 of girls know chess.Find the number of students who know chess.

Answer 1

Denote x number of biys y number of girls

x=y+40

x+y=60

 

(3/4)x+(5/7)y know chess.

First we have to find x and y from

x-y=40
x+y=600

2x=640

x=320 (number of boys)

2y=560

y=280 (number of girls)

Now you can coumpute (3/4)320+(5/7)280=3*80+5*40=440.