Two boats have same speed of 10 km/hr in still water. First boat starts from a point P and goes upstream. At the same time, second boat starts from same point P and goes downstream. After 3 hours, the sum of distances covered by them is 60 km. What is the speed of the stream (in km/hr)?
Solution
Correct Answer: Option E
Let the speed of stream be V km/hr.
⇒ Upstream speed = (10 – V) km/hr
⇒ Downstream speed = (10 + V) km/hr
We know, Distance = Speed × Time
Distance travelled by first boat in 3 hours upstream = 3 × (10 – V) km
Distance travelled by second boat in 3 hours downstream = 3 × (10 + V) km
⇒ Total distance travelled = 3 × (10 – V) km + 3 × (10 + V) km = 60 km
⇒ 30 – 3V + 30 + 3V = 60
⇒ 60 = 60
We see it is an identity, and any value of V would satisfy it.
∴ Speed of stream cannot be determined uniquely.
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