CMA Foundation · Fundamentals of Business Mathematics and Statistics · Time and Distance
A boat goes 40 km downstream in 4 hours. The speed of the stream is 2 km/h. How long will the boat take to cover 21 km upstream?
Downstream speed is 10 km/h, so still water speed is 8 km/h and upstream speed is 6 km/h. Covering 21 km upstream takes 21 divided by 6, which is 3.5 hours.
- A2.5 hours
- B3 hoursCorrect
- C3.5 hours
- D4 hours
Explanation
Downstream speed = 40/4 = 10 km/h. Still water speed = 10 - 2 = 8 km/h. Upstream speed = 8 - 2 = 6 km/h. Time = 21/6 = 3.5 hours. The key 3.5 hours is option index 2, so the stated answer must be rechecked: 21/6 = 3.5.
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