A boat goes 27 km upstream and 33 km downstream in 6 hours. In the same time it can go 36 km upstream and 22 km downstream. How much time will it take to go 36 km upstream and 44 km downstream?
A boat goes 27 km upstream and 33 km downstream in 6 hours. In the same time it can go 36 km upstream and 22 km downstream. How much time will it take to go 36 km upstream and 44 km downstream? Correct Answer 8 h
Given:
27km upstream and 33km downstream = 6 hours
36km upstream and 22km downstream = 6 hours
Formula:
Speed of boat = a kmph and Speed of stream = b kmph
Speed of upstream = (a - b) kmph
Speed of downstream = (a + b) kmph
Calculation:
⇒ 33/(a + b) + 27/(a - b) = 6
⇒ 22/(a + b) + 36/(a - b) = 6
Then,
⇒ 33/(a + b) + 27/(a - b) = 22/(a + b) + 36/(a - b)
⇒ 11/(a + b) = 9/(a - b)
⇒ 11a - 11b = 9a + 9b
⇒ 2a = 20b
⇒ a = 10b
Then,
⇒ 33/(10b + b) + 27/(10b - b) = 6
⇒ 3/b + 3/b = 6
⇒ b = 1
⇒ a = 10
Speed downstream = 10 + 1 = 11 kmph
Speed upstream = 10 - 1 = 9 kmph
Then,
⇒ ? = 44/11 + 36/9
⇒ ? = 4 + 4
⇒ ? = 8
∴ it will take 8 hours to go 36 km upstream and 44 km downstream.