math
posted by Im on .
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.

b+g = 40
4/5 b + 2/3 g = 40n
2/3 b + 2/3 g = 2/3 * 40
4/5 b + 2/3 g = 40n
(4/5  2/3)b = 40n  2/3*40
2/15 b = 40/3  n
b = 5(403n)/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