In one hour, a boat goes 20 km along the stream and 18 km against the stream. The speed of the boat in still water (in km/hr) is:

Options
- 17
- 19
- 21
- 23

CORRECT ANSWER : 19

Discussion Board
Solution

Given details ,
Distance of downstream D''d = 20km
Distance of upstream D''u = 18km
Time for both downstream and upstream is 1 hour
STEP 1 = Find speed of downstream and upstream first.
downstream speed S''d = 20/1 = 20
Upstream speed S''u = 18/1 = 18
STEP 2 ,
Use the boat in still water formula that is 1/2× (downstream speed +upstream speed) and substitute it.

=1/2× {20+18}
=1/2 × (38)
= 19 kmph

GK 07-30-2021 08:53 AM

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