how to solve 150 pupils went to concert.3/4 of the number of boys was equal to 1/7 of the number of girls. how many boys went to the concert?

Answer 1

boys --- b
girls --- g

b+g = 150

(3/4)b = (1/7)g
3b/4 = g/7
4g = 21b
g = 21b/4

sub into the first
b+g = 150
b + 21b/4 = 150
times 4
4b + 21b = 600
25b=600

b = 24
then g = 21(24/4) = 126

24 boys and 126 girls went to the concert

check:
is 24+126 = 150 ? , YES
is (3/4)(24) = (1/7)(126) ? , YES, both are 18

(must have been a Justin Bieber concert)