Question

A boat can go 20 km downstream and 30 km upstream in 2 hours 20 minutes. Also it can go 10 km. downstream and 8 km. upstream in 49 minutes. What is the speed of the boat downstream (in km/h)?

Options

• 24

• 20

• 18

• 16

Answer 1

24

Explanation:

`20/(x + y) + 30/(x - y)` = 2 h 20 m

`10/(x + y) + 8/(x - y)` = 49 m

(i) × 4 – (ii) × 15

`80/(x + y) - 150/(x + y) = (9h  20m) - (12h  15m)`

`70/(x + y)` 2h 55m = `35/12`

⇒ `x + y` = 24 kmph.