A takes 2 hours 30 minutes more than B to walk 40 km. If A doubles his speed, then he can make it in 1 hour less than B. How much time (in hours) does A require for walking a 40 km distance?

7

Let, Speed of A is S km/h

Time taken by A to cover the distance \(\frac{40}{S}\) hour

Time taken by B =  ( \(\frac{40}{S}\)- 2.5) hours

When A doubles his speed time taken by A = \(\frac{40}{2S}\) hour

Accordingly,

 ( \(\frac{40}{S}\)- 2.5)  – \(\frac{40}{2S}\)= 1

\(\frac{40}{S}\) – \(\frac{40}{2S}\)= 3.5

\(\frac{40}{2S}\) = \(\frac{7}{2}\)

S = \(\frac{40}{7}\)

Time taken by A to cover the distance 40 ÷ \(\frac{40}{7}\)

= 7 hours

So ,  A needs 7 hours to walk a 40 km distance.