Multiple choice

Arjun travelled $240$ miles at a certain speed. If he were to increase his speed by $20mph$, it would have taken him $2$ hours less to travel same distance. What was his speed in mph?

  1. 30

  2. 40

  3. 50

  4. 60

  5. 80
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let speed be v. 240/v - 240/(v+20) = 2. 120/v - 120/(v+20) = 1. 120(v+20-v) = v(v+20). 2400 = v^2 + 20v. v^2 + 20v - 2400 = 0. (v+60)(v-40) = 0. Speed = 40.

AI explanation

Let the original speed be v mph; the time taken originally is 240/v hours, and with the increased speed it is 240/(v + 20) hours. Setting up the equation based on the time difference, 240/v minus 240/(v + 20) equals 2. Solving the quadratic equation v^2 + 20v minus 4800 equals 0 gives v equal to 40. The original speed was 40 mph.

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