Question

a boat can go 51mph in still water. It takes as long to go 640 miles upstream as it does to go downstream 720 miles. How fast is the current going?

Answer 1

@welshfella do you know?

Answer 2

Going downstream the boats speed is 51 + v where v is the speed of the current
Going upstream its speed will by 51 - v

Answer 3

Going downstream
speed = distances / time

51 + v = 720 / t

upstream
51 - v = 640 / t

Answer 4

@welshfella they don't give us the time though.

Answer 5

so downstream t = 720 / (51+ v)
uostream t = 640 / (51 - v)

as the times are the same

720 / (51 + v) = 640 / (51 - v)

solve for v