Benny spent 1/5 of his money on 4 pineapples and 8 mangoes. The cost
of a pineapple was 4 times that of a mango. Benny bought some more
pineapples with 1/2 of his remaining money. How many pineapples did
Benny buy in all?
Without loss of generality, say Benny has $120.
He just spent 24 dollars on 4 pineapples and 8 mangoes.
Since a pineapple is 4 times a mango, Benny spent 1 dollar per mango and 4 dollars per pineapple.
He now has 96 dollars, and he spends $48 on pineapples, accounting for 12 pineapples.
He has bought 12+4 = 16 pineapples.