A takes 4 h more than the time taken by B to walk D km.

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A takes 4 h more than the time taken by B to walk D km. If A doubles his speed, he can make it in 2 h less than that of B. How much time does B require for walking D km?

1. 8 h
2. 4 h
3. 6 h
4. 9 h

Correct Option: A

Let B takes x h to walk D km.
Then, A takes ( x + 4 ) h to walk D km.
With doube of the speed,
A will take ( x+ 4)/2 h.

According to the question,
x - (x + 4)/2 = 2
⇒ 2x - (x + 4) = 4
⇒ 2x - x - 4 = 4
∴ x = 4 + 4 = 8 h