A boat can travel 104 km downstream in 8 hours. If the speed of the stream is 2 km/h, then find in what time will it be able to cover 13 km upstream?

$1\frac{4}{9}$hours

We know that,

Downstream speed = Speed in still water + Speed of stream

Distance = Speed × Time 

We have,

The boat can travel 104 km downstream in 8 hours.

Speed of stream = 2 km/h

= Let the speed of the boat in still water be a and the speed on the stream be b.

= 104/(a + b) = 8

= a + b = 13

= a = 2 (given)

= a = 13 – b = 13 – 2 = 11

= Upstream speed = 11 – 2 = 9 km/h

= Distance = Speed × Time 

= 13 = 9 × Time

= Time = 13/9 = $1\frac{4}{9}$ hours