Question : A boat can row 24 km in 6 hours in still water It can row 56 km downstream and 30 km upstream in 38 hours. What is the speed of the stream?
Option 1: 3 km/hr
Option 2: 5 km/hr
Option 3: 3.5 km/hr
Option 4: 4 km/hr
Correct Answer: 3 km/hr
Solution :
Let the boat still in the water as B and the speed of the stream as S.
⇒ B = $\frac{24}{6}$ = 4 km/hr
Downstream speed = (B + S) = (4 + S) km/hr
Upstream speed = (B – S) = (4 – S) km/hr
According to the question,
⇒ For downstream, 56 = (4 + S) × t
1
⇒ For upstream, 30 = (4 – S) × t
2
⇒ Total time = t
1
+ t
2
= 38
Now, t
1
= $\frac{56}{4 + S}$ and t
2
= $\frac{30}{4 – S}$
⇒ $\frac{56}{4 + S}$ + $\frac{30}{4 - S}$ = 38
Solving this, we get $S = 3$ km/hr
Hence, the correct answer is 3 km/hr.
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