Multiple choice

A jogger desire to run a certain course in ¼ less time than he usually takes, by what per cent must be increase his average running speed to accomplish the goal

  1. 50%

  2. 20%

  3. 25%

  4. 33 1/3%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let original time be T and original speed be S. Distance D = S * T. New time = 3/4 T. New speed S' = D / (3/4 T) = 4/3 S. The increase in speed is (4/3 - 1)S = 1/3 S. Percentage increase = (1/3) * 100 = 33.33%.

AI explanation

Let the original time be t and the original speed be s, so the distance is s multiplied by t. The new time is t minus t/4, which equals 3t/4, and let the new speed be S, so the distance is also S multiplied by 3t/4. Equating the distances gives s times t equals S times 3t/4, so S equals 4s/3. The increase in speed is S minus s, which is s/3, and converting this to a percentage of the original speed gives (1/3) times 100, resulting in an increase of 33 1/3 percent.

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