Question

A river runs at 3 kmph. if the time taken by a man to row his boat upstream is twice the time taken by him to row it downstream , then at what speed can he row his boat in still water?​

Answer 1

Given :-

• Speed of River or, Speed of water = 3km/h.
• Time taken by a man to row his boat upstream is twice the time taken by him to row it downstream .

Concept Used :-

• Downstream Speed = (Speed of Boat in Still water + Speed of Water in The river).
• Upstream Speed = (Speed of Boat in Still water - Speed of Water in The river).
• Time = Distance / Speed .

Solution :-

Let Total Distance covered is D , and Speed of boat in Still water is X km/h.

Than,

→ Downstream Speed = (x + 3) km/h.

→ Downstream Time = D/S = D/(x + 3) km/h.

→ Upstream Speed = (x - 3) km/h.

→ Upstream Time = D/S = D/(x - 3) km/h.

Now, it is Given That , upstream team is twice of downstream time ,

So,

→ 2((D/(x + 3)) = D/(x - 3)

Cancelling D from Both Numerator,

→ 2(x - 3) = (x + 3)

→ 2x - 6 = x + 3

→ 2x - x = 3 + 6

→ x = 9 km/h.

Hence, speed of boat in still water is 9km/h.

Answer 2

Step-by-step explanation:

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Upstream speed = x-3

Downstream speed =x+3

Let " t " be time.

Comparing with upward stream , when the boat coming downwards then speed will be doubled. So "2t" for downstream and "t" for upwardsteam.

(x - 3)×2×t=(x - 3)×t

Cancelling "t" on both sides

(x-3)2=(x+3)

2x-6=x+3

2x-x=6+3

x=9

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