A boat in still water travels at a speed of 24 kmph. It goes 40 km downstream in 1 hour 20 minutes. The time taken by it to cover a 45 km distance upstream will be -

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Question: A boat in still water travels at a speed of 24 kmph. It goes 40 km downstream in 1 hour 20 minutes. The time taken by it to cover a 45 km distance upstream will be -

Solution:
downstream speed = 40/(4/3) kmph
= 30 kmph

speed of stream = 30 - 24 = 6 kmph

∴ speed upstream = 24 - 6 = 18 kmph

time to cross 45 km is = 45/18 hour
= 2.5 hour
= 2 hour 30 minutes.