A boat can move 9km/hr in still water. If the river is running 3km/hr ,it takes 90 minutes to move to a place and back. How far is the place?
Answers
Given:
Speed of the boat in still water =9km/hr.
Speed of the river =3km/hr.
Downstream=9+3=12km/hr.
Upstream=9-3=6km/hr.
x/12+x/6=90/60
6x=36
x=6km/hr.
Solution :-
Let us assume that, the the place is x km far .
So,
→ Distance coved in downstream = x km
→ Speed of boat in downstream = Spee of boat in still water + river speed = 9 + 3 = 12 km/h
then,
→ Time taken in downstream = Distance / speed = (x/12) hours .
now,
→ Distance coved in upstream = x km
→ Speed of boat in upstream = Spee of boat in still water - river speed = 9 - 3 = 6 km/h
then,
→ Time taken in upstream = Distance / speed = (x/6) hours .
A/q,
→ Time taken in downstream + Time taken in upstream = 90 minutes = 90/60 = 3/2 hours
→ (x/12) + (x/6) = 3/2
→ (x + 2x)/12 = 3/2
→ (3x/12) = 3/2
→ (x/4) = (3/2)
→ 2x = 4 * 3
→ x = 6 km (Ans.)
Hence the place is 6 km far .
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