The speed of a boat in still water is 30 km/h. If the boat covers 60 km downstream in 1 hour 30 minutes, then what is the time taken by the boat to cover 60 km upstream?

3 hours

Let speed of stream = S km/h

Speed in downstream = ( 30 + S ) km/h

Speed = \(\frac{Distance}{Time}\)

According  to question ,

 \(\frac{60}{30 - S }\) = 1\(\frac{1}{2}\)

\(\frac{60}{30 - S }\) = \(\frac{3}{2}\)

S = 10 km/h

Speed in upstream = 30 - 10 = 20 km/h

Time taken = \(\frac{60}{20 }\) = 3 hours