If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 km…
2026
If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 km per hour, then the speed of the boat in still water is:
- A.
14 km per hour
- B.
13 km per hour
- C.
16 km per hour
- D.
15 km per hour
Attempted by 270 students.
Show answer & explanation
Correct answer: B
Step 1: Convert the time from minutes to hours. Since 42 minutes is 42/60 = 0.7 hours.
Step 2: Calculate the upstream speed. The boat travels 7 km in 0.7 hours, so the upstream speed is 7 / 0.7 = 10 km/h.
Step 3: Recall that upstream speed = speed of boat in still water – speed of stream.
Step 4: Let the speed of the boat in still water be x km/h. Then, x – 3 = 10.
Step 5: Solve for x: x = 10 + 3 = 13 km/h.