Walking 5/4 of his usual rate, a boy reaches his school 4 min early. Find his usual time to reach the school?	Choices: A) 22 B) 99 C) 27 D) 28 E) 20

Rationale: "speed ratio = 1 : 5 / 4 = 4 : 5 time ratio = 5 : 4 1 - - - - - - - - 5 4 - - - - - - - - - ? 20 m . answer : e"
Answer: E