Answer:
14 boys paid for the full year fee and 4 boys paid for the partial year fee
Explanation:
Create a system of equations, where x is the number that paid for the $24 fee and y is the number that paid for the $16 fee:
24x + 16y = 400
x = y + 10
Solve by substitution by plugging in y + 10 as x:
24x + 16y = 400
24(y + 10) + 16y = 400
Solve for y:
24y + 240 + 16y = 400
40y + 240 = 400
40y = 160
y = 4
Then, plug in 4 as y to find x:
x = y + 10
x = 4 + 10
x = 14
So, 14 boys paid for the full year fee and 4 boys paid for the partial year fee.