Problem: if tim had lunch at $ 50.50 and he gave 10 % tip , how much did he spend ?
Rationale: "the tip is 20 % of what he paid for lunch . hence tip = 20 % of 50.50 = ( 10 / 100 ) * 50.50 = $ 5.05 total spent 50.50 + 5.05 = $ 55.55 correct answer d"
annotated_formula: add(50.50, divide(multiply(50.50, 10), const_100))