Question

The speed of a boat in still water is 15 km/h and speed of stream is 5 km/h. The boat goes x km downstream and then returns back to the point of start is ______.

विकल्प

• `(x/20 - x/5)` hrs

• `(x/10 - x/20)` hrs

• `(x/20 + x/10)` hrs

• `(x/20 - x/10)` hrs

Answer 1

The speed of a boat in still water is 15 km/h and speed of stream is 5 km/h. The boat goes x km downstream and then returns back to the point of start is `underlinebb((x/20 + x/10) hrs)`.

Explanation:

Given the speed of boat in still water = 15 km/h

Speed of stream = 5 km/h

∴ Speed of boat upstream

= 15 – 5

= 10 km/h

And the speed of boat downstream

= 15 + 5

= 20 km/h

∴ Time is taken by boat x km downstream

@ 20 km/h = `"Distance"/"Speed"` = `x/20` hrs

Time is taken by boat x km upstream

@ 10 km/h = `x/10` hrs

Thus, the total time taken by boat goes x km downstream and then return to the point of start = `(x/20 + x/10)` hrs.