A certain protective additive increases from 50 days to 60 days the time between required maintenance checks on an industrial vehicle. By what percent is the time between maintenance checks increased by using the additive?	Options
A) 25 %  B) 33 1 / 3 %  C) 50 %  D) 66 2 / 3 %  E) 20 %

Rationale: "general formula for percent increase or decrease , ( percent change ) : percent = change / original ∗ 100 so , the time between maintenance checks increased by 60 − 50 / 50 ∗ 100 = 20 answer : e ."
Answer: E