Boat and stream?

Question

the respective ratio between the speed of the boat upstream and speed of the boat downstream is 2:3. what is the speed of the boat in still water if it cover 42 km downstream in 2h 20 mins?

Answer

boat speed = B, stream speed = S

(B + S)/3 = (B - S)/2

2B + 2S = 3B - 3S  Subtract (2B + 2S).

0 = B - 5S

B = 5S

Given: (B + S) = 42km/140m  Now substitute B = 5S.

6S = 42/140  Divide by 6.

S = 7/140 km/min  Multiply by 5.

B = 35/140 km/min x 60 min/hr = 15 km/hr

Boat and stream?

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