A walks at 10 kmph and 10 hours after his start, B cycles after him at 20 kmph. How far from the start does B catch up with A?
Choose the correct choice from the following answers.
A) 100 km B) 150 km C) 50 km D) 120 km E) 200 km

Rationale: "suppose after x km from the start b catches up with a . then , the difference in the time taken by a to cover x km and that taken by b to cover x km is 10 hours . x / 10 - x / 20 = 10 x = 200 km answer is e"
Answer: E