how many milliliters of pure acid do I need to add to 15ml of 50% acid to make 85% acid solution

Question

how many milliliters of pure acid so i need to add to 15ml of 50% acid to make 85% acid solution

Answer 1

pure acid is considered to be 100% acid.

(x ml)(100%) + (15 ml)(50%) = (15 ml + x ml)(85%)

100x + 750 = 1275 + 85x

15x = 525

x = 35 ml of 100% (pure) acid is needed