Answer:
20
Step-by-step explanation:
The cost of the x mangoes was ...
c = 10(x/4)
The revenue from the sale of mangoes was ...
r = 20(x-5)/5
The profit is the difference between revenue and cost:
10 = r - c = 20(x -5)/5 -10(x/4) = 1.5x -20 . . . . substitute and simplify
30 = 1.5x . . . . . add 20
20 = x . . . . . . . .divide by 1.5
The trader bought 20 mangoes.
_____
Check
He paid 20(10/4) = 50 naira. He sold the 15 good mangoes for 20/5(15) = 60 naira, so made a 10 naira profit.
