Multiple choice

The speed of train A is 16 km per hour less than the speed of train B. To cover a distance of 384 km, B takes 4 hrs less time than A. What is the speed (in km/hr) of train B?

  1. 50

  2. 45

  3. 48

  4. 32
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let B's speed = x km/h. Then A's speed = (x - 16) km/h. Time for A = 384/(x-16), time for B = 384/x. B takes 4 hours less: 384/(x-16) - 384/x = 4. Solving: 384x - 384(x-16) = 4x(x-16). 384x - 384x + 6144 = 4x² - 64x. 4x² - 64x - 6144 = 0. x² - 16x - 1536 = 0. (x - 48)(x + 32) = 0. x = 48 (positive). B's speed = 48 km/h.

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