A motor boat covers the distance between the two sport on the river in `9 h and 13 h` down stream and upstream respectively. Find the time required by the boat to cover this distance in still water.

Explanation

Let (u) be the velcity of boat in still water and (v) be the velcity of river. Let (x) be the distance between two given spets. As per question.
For downstream, `u +v =x/9`
For upstream, `u-v =x/(13)`
On adding, `2u =x/9 +x/(13) =(22x)/(117) or u =(11x)/(117)`
Time taken by boat to cover distance (x) in still
water is `t=x/u = x /(11 x//117) =10.63 h`.