A motorboat covers a given distance in 6 hr moving downstream on a river. It covers the same distance in 10 hr moving upstream. If the time it takes to cover the same distacne in still water is t, then write `(t)/(2.5)` in hrs.

Answer

3

Explanation

`d = (v + u) 6` …(1)
`d = (v - u) 10` … (2)
`((v + u)/(v - u)) (6)/(10) = 1`
`v = 4u`
`d = (5u) 6 " " d = 30 u`
`d = vt`
`t = (d)/(v) = (30u)/(4) = 7.5 hr`