A takes 3 hours more than B to walk d km, but if A doubles his speed, then he can make it in 1 hour less than B. How much time does A require for walking d km?

Question: A takes 3 hours more than B to walk d km, but if A doubles his speed, then he can make it in 1 hour less than B. How much time does A require for walking d km?

Solution:
Let,
B takes "t" hours to walk "d" km.

Then, A takes (t + 3) hours to walk d km.
With double speed, A will take = (1/2)(t + 3) hours.

ATQ,
t - (1/2)(t + 3) = 1
⇒ {2t - (t + 3)}/2 = 1
⇒ 2t - t - 3 = 2
∴ t = 5

∴ B takes 5 hours to walk d km.

∴ A takes (5 + 3) = 8 hours to walk d km.