A ferry runs at 24 knots for 3 hours, then 15 knots for 2 hours. What is its average speed? Show your working
Reasoning Trace
This is a routine kinematics question about mean speed. The user wants the average across two legs that differ in both speed and duration.
Mean speed is total distance divided by total time.
Working through it:
•First leg: 24 knots for 3 hours. Distance = 24 × 3 = 72 nm
•Second leg: 15 knots for 2 hours. Distance = 15 × 2 = 30 nm
Total distance = 72 + 30 = 102 nm. Total time = 3 + 2 = 5 hours
Mean speed = 102 / 5 = 20.4 knots
Worth flagging: that is not the plain mean of 24 and 15, because the legs are unequal.
One decimal place is enough — the inputs carry two significant figures.
No lookup is needed for this one, so I can answer directly and lay out each arithmetic step in order.
Mean Speed Calculation
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