Question

A boat can go 30 km downstream and 24 km upstream in 2 hours 27 minutes. Also, it can go 20 km downstream and 8 km upstream in 74 minutes. What is the speed of the boat in still water in km/h?

पर्याय

• 18

• 20

• 24

• 22

Answer 1

22

Explanation:

`30/(x + y) + 24/(x - y)` = 2 h 27 m  ......(i)

`20/(x + y) + 8/(x - y)` = 1 h 14 m  ......(ii)

(i) – (ii) × 3

`30/(x + y) - 60/(x + y)` = (2 h 27 m) – (3 h 42 m)

`30/(x + y)` = 1 h 15 m = `5/4`

`x + y` = 24  ......(iii)

`24/(x - y)` = 1 h 12 m = `6/5`

`x - y` = 20  ......(iv)

Now, `x = (24 + 20)/2` = 22 kmph