Explanation:
First find the total weight of the male students
5/3 = x / 870 cross multiply
4350 = 3x
x = total boys' weight = 1450 kg
if the mean is GREATER THAN 80 then
1450 / n > 80 where n is the number of boys
1450/80 > n
n< 18.125 max number would be 18 boys