Angelo bought 14 apples and 6 bananas
Solution:
Let "a" be the number of apples bought
Let "b" be the number of bananas bought
Cost of 1 apple = $ 0.50
Cost of 1 banana = $ 0.75
He bought 20 pieces of fruit. Therefore,
number of apples bought + number of bananas bought = 20
a + b = 20 -------- eqn 1
He spent $ 11.50. Therefore, we frame a equation as:
number of apples x Cost of 1 apple + number of bananas x Cost of 1 banana = 11.50

0.50a + 0.75b = 11.50 ------- eqn 2
Let us solve eqn 1 and eqn 2
From eqn 1,
a = 20 - b ------ eqn 3
Substitute eqn 3 in eqn 2
0.50(20 - b) + 0.75b = 11.50
10 - 0.5b + 0.75b = 11.50
0.25b = 11.50 - 10
0.25b = 1.5
Divide both sides of equation by 0.25
b = 6
Substitute b = 6 in eqn 3
a = 20 - 6
a = 14
Thus he bought 14 apples and 6 bananas