Question

A man can row 12 kilometre/hour in still water if the speed of the current is 3 kilometre/hour he takes 4 hours more in upstream than in the down stream.what is the distance( in kilometre)?​

Answer 1

The the distance covered by the man be 'x km'

During upstream

Speed of man = (12-3)km/h

                        = 9 km/h

During downstream

Speed of man = (12+3)km/h

                        = 15 km/h

Speed = $\frac{Distance}{Time}$

hence, Time = $\frac{Distance}{Speed}$

Time taken in upstream = $\frac{x}{9}$

Time taken in downstream = $\frac{x}{15}$

The man takes 4 hours more in upstream than in down stream

Hence,

$\frac{x}{9}$ -  $\frac{x}{15}$ = 4

6x = 4×15×9

x = 90 km

HOPE IT HELPS !!