Ramu swims a distance of 3 km each upstream and downstream. The total time taken is one hour. If the speed of the stream is `4` km/h, then find the speed of Ramu in still water.

Options

A. 12 km/h
B. 9km/h
C. 8 km/h
D. 6 km/h

Answer

C

Explanation

Let the speed of Ramu = x km/h
Total time taken is = 1 hour
That is,
`(3)/(x-4) + (3)/(x+4) = 1`
`(3x+12+3x-12)/(x^(2) - 16) = 1`
`6x=x^(2) - 16`
`x^(2) - 6x-16 = 0`
`x^(2) - 8x+2x-16= 0`
`x(x-8) + 2(x-8) = 0`
`(x-8) (x+2) = 0`
`x = 8` km/h ( `: '` speed cannot be `- 2` km/h).