Average speed and upstream/downstream

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Learn it Average speed = TOTAL distance ÷ TOTAL time (stops count as time). Boats: downstream speed = boat + current, upstream speed = boat − current. So current = (down − up) ÷ 2 and boat = (down + up) ÷ 2.

Example: A boat goes 18 km/h downstream and 12 km/h upstream. Find its speed in still water and the current.

Boat speed = $(18 + 12) \div 2 = 15$ km/h.
Current = $(18 - 12) \div 2 = 3$ km/h.
Check: $15 + 3 = 18$ and $15 - 3 = 12$ ✓.

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