Multiple choice

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?

  1. 9

  2. 7

  3. 6

  4. 5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let B's time be t hours for 40 km. Then A's normal time = t + 2.5 hours, so A's normal speed = 40/(t + 2.5). When A doubles speed: 2 × 40/(t + 2.5) = 40/(t - 1). This gives 2/(t + 2.5) = 1/(t - 1), so 2t - 2 = t + 2.5, giving t = 4.5 hours. Therefore A requires 4.5 + 2.5 = 7 hours.

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