Walking 9/8 of his usual rate, a boy reaches his school 4 min early. Find his usual time to reach the school?
Answers
A) 22 B) 99 C) 27 D) 36 E) 20

Rationale: "speed ratio = 1 : 9 / 8 = 8 : 9 time ratio = 9 : 8 1 - - - - - - - - 9 4 - - - - - - - - - ? 36 m . answer : d"
Answer: D