Speed of motorboat in still water is 45 kmph If the motorboat travels 80 km along the stream in 1 ho......

Speed of motorboat in still water is 45 kmph. If the motorboat travels 80 km along the stream in 1 hour 20 minutes, then the time taken by it to cover the same distance against the stream will be :

The speed of motorboat in still water, x = 45 km/h
Downstream speed = 80/ [1 + (20/60)] = 80/[(1 + 1/3)]
= (80 × 3)/4 = 60 km/h
x + y = 60
45 + y = 60
y = 15 km/h
Upstream speed = x – y = 45 – 15
= 30 km/h
Time = Distance/ Upstream speed
= 80/30 = 8/3 h = 2 hours 40 minutes

By: Manpreet kaur