✔ 最佳答案
suppose x = no. of female, y = no. of male
x+y =40
0.5 x + 1/3 y = 16
sub x= 40- y
0.5 (40-y) + 1/3 y =16
20-0.5y +1/3 y =16
20-1/6y = 16
4= 1/6y
so y = 24
x = 16
check ok: 16*0.5 + 1/3 * 24 = 16
the key is to rearrange the equation so you have just a number on one side and only one symbol on the other.
hope it helps