Multiple choice

A boat goes 8 km in one hour along the stream and 2 km in one hour against the stream. The speed (in km/hr) of the stream is

  1. 2

  2. 3

  3. 4

  4. 5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Downstream speed (boat + stream) = 8 km/hr. Upstream speed (boat - stream) = 2 km/hr. Stream speed = (downstream - upstream)/2 = (8-2)/2 = 3 km/hr. This is derived by adding the two equations: (b+s) + (b-s) = 8+2, which gives 2b = 10, then s = 8-b = 3.

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