A swimmer swims 5 km upstream and 3 km downstream in 1 hour. If the speed of the stream is 3 kmph, find the swimmer's speed.
A
6 kmph
B
5 kmph
C
4.5 kmph
D
7.5 kmph
Correct Option - A
Explaination
Let swimmer's speed=x kmph
Time taken to swim downstream
= 5/(x-3)
Time taken to swim upstream
= 3/(x+3)
[5/(x-3)]+[3/(x+3)] = 2
5x+15+3x-9 = 2(x²-9)
2x²-8x-24=0
x²-4x-12=0
(x-6)(x+2)=0
x can't be -2
Hence, x=6 kmph