Problem: what quantity of water should be added to reduce 20 liters of 80 % acidic liquid to 20 % acidic liquid ?
Rationale: "acid in 20 liters = 80 % of 20 = 16 liters suppose x liters of water be added . then 16 liters of acid in 20 + x liters of diluted solution 20 % of 20 + x = 16 20 + x = 80 x = 60 liters answer is c"
annotated_formula: subtract(divide(multiply(multiply(20, divide(80, const_100)), const_100), 20), 20)