Question

A boat goes 30km upstream and 28km downstream in 10 hours. In 7 hours, it can go 21 km upstream and 21 km downstream then to return downstream to the same spot. Find the speed of stream and that of the boat in still water and speed of the stream.
If the boat's speed is b and the stream's speed is s, then
since time = distance/speed,
30/(b-s) + 28/(b+s) = 10
21/(b-s) + 21/(b+s) = 7
I suspect a typo.

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