# math

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A river has a current of 4 mph. Find the speed of Simon’s boat in still water if it goes 40 miles downstream in the same time as 24 miles upstream.

• math -

speed of boat ---- x mph
speed downstream = x+4
speed upstream = x-4

time upstream = 24/(x-4)
time downstream = 40/(x+4)

40/(x+4)= 24/(x-4)
cross-multiply
40x - 160 = 24x + 96
16x = 256
x = 16

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