Multiple choice

A car travelled 715 km at a uniform speed. If the speed of the car had been 10 km/hr more, it would have taken 2 hours less to cover the distance. The original speed of the car was

  1. 45 km/hr

  2. 55 km/hr

  3. 60 km/hr

  4. 65 km/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let speed be v. 715/v - 715/(v+10) = 2. 715(v+10-v) = 2v(v+10). 7150 = 2v^2 + 20v. v^2 + 10v - 3575 = 0. Solving gives v=55.

AI explanation

Let the original speed be x km/hr, so the original time is 715/x hours and the new time is 715/(x+10) hours. Using the time difference, 715/x - 715/(x+10) = 2, which simplifies to (x+10)(x-55) = 0. Since the speed cannot be negative, the original speed is 55 km/hr.

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