A boy is travelling from his home to school at 4 km/hr and reached 7 min late. Next day he traveled at 8 km/hr and reached 8 min early. Distance between home and school?
Answers:  A) 2 km  B) 3 km  C) 4 km  D) 5 km  E) 6 km

Rationale: "let the distance be x t 1 = x / 4 hr t 2 = x / 8 hr difference in time = 7 + 8 = 15 = 1 / 4 hr x / 4 - x / 8 = 1 / 4 x / 8 = 1 / 4 x = 2 km answer is a"
Answer: A