A boat covers 143 km upstream in 13 hours and the same distance downstream in 11 hours. What is the speed (in km/hr) of the boat in still (without stream) water?
Solution
Correct Answer: Option B
Let,
the speed (in km/hr) of the boat in still (without stream) water is x km/hr and speed of stream is y km/hr
Now,
143/(x - y) = 13
⇒ 13 (x - y) = 143
⇒ x - y = 11..........(i)
143/(x + y) = 11
⇒ 11 (x + y) = 143
⇒ x + y = 13..........(ii)
(i) + (ii) ⇒
x - y + x + y = 13 + 11
⇒ 2x = 24
∴ x = 12 km/hr
the speed (in km/hr) of the boat in still (without stream) water is x km/hr and speed of stream is y km/hr
Now,
143/(x - y) = 13
⇒ 13 (x - y) = 143
⇒ x - y = 11..........(i)
143/(x + y) = 11
⇒ 11 (x + y) = 143
⇒ x + y = 13..........(ii)
(i) + (ii) ⇒
x - y + x + y = 13 + 11
⇒ 2x = 24
∴ x = 12 km/hr
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