The effective speed of a boat travelling downstream is 20 kmph, whereas it is 10 kmph upstream. What is the speed of the stream current in kmphr?

The effective speed of a boat travelling downstream is 20 kmph, whereas it is 10 kmph upstream. What is the speed of the stream current in kmphr?

A 3

B 4

C 5

D None of these

Solution

Correct Answer: Option C

let,

boat speed = x

stream speed = y

Thus,

x + y = 20 ..... (1)

x - y = 10 ........ (2)

Now, from (1) + (2)

2x = 30

x = 15

putting value of x in eq. (1)

15 + y = 20

y = 20 - 15 = 5