Multiple choice

The distance of the School and house of Suresh is 80 km. One day he was late by 1 hour than the normal time to leave for the college, so he increased his speed by 4 km/h and thus he reached to college at the normal time. What is the changed speed of Suresh?

  1. 28 km/h

  2. 25 km/h

  3. 20 km/h

  4. 24 km/h
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let original speed be x km/h. Distance = 80 km. Normal time = 80/x hours. New speed = (x+4) km/h. New time = 80/(x+4) hours. Since new time is 1 hour less: 80/x - 80/(x+4) = 1. Solving: 80(x+4) - 80x = x(x+4), 320 = x² + 4x, x² + 4x - 320 = 0, (x+20)(x-16) = 0, x = 16 km/h. Changed speed = 16+4 = 20 km/h.

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