Multiple choice

A boat moves downtream at the rate of 1 km in 7.5 minute and up stream at the rate of 5 km an hour. The speed of boat in (km/hr) in still water is.

  1. 6

  2. 7

  3. 6.5

  4. 7.5

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Downstream speed (8 km/hr) is boat + current, upstream speed (5 km/hr) is boat - current. Still water speed = (8 + 5) / 2 = 6.5 km/hr. Current speed is (8 - 5) / 2 = 1.5 km/hr. This formula works for all boat-stream problems.