How many ounce of acid must be added to 20 ounce of solution that is 5% acid to strengthen it to a solution that is 24% acid?

If 20 ounces will give you 5% acidity, you can assume that every 4 ounces will give you 1% acidity (Divide 20 by 5).

If 20 = 5
40 = 10
80 = 20.
84 = 21.
88 = 22.
92 = 23.
96 would be 24% — the answer you’re looking for.