There are 40 children in a class. n of them do not wear spectacles. 4/5 of the boys and 2/3 of the girls wear spectacles. Express the number of boys who wear spectacles in terms of n.

3 answers

b+g = 40
4/5 b + 2/3 g = 40-n

2/3 b + 2/3 g = 2/3 * 40
4/5 b + 2/3 g = 40-n

(4/5 - 2/3)b = 40-n - 2/3*40
2/15 b = 40/3 - n
b = 5(40-3n)/2 = 100 - 15n/2

Check: suppose n = 10
b = 25
g = 15

boys who wear: 20
girls who wear: 10

Thank you, Steve.

I dun understand