Question

A man can swim in still water with a speed of $25m/min$. If the speed of the stream is $15m/min$, and its width is $100m$, the time taken to cross the stream by shortest route and the quickest route is

• A. $3min$, $5min$
• B. $5min$, $4min$
• C. $3min$, $4min$
• D. $4min$, $5min$

Answer 1

Answer: (B)

$5min$, $4min$

In quickest route $t=$ $\frac{100m}{25m/min}$ = $4min$

In shortest route $t=$ $\frac{100}{\sqrt{{25}^2-{15}^2}}=\frac{100}{20}$ = $5min$