If a person goes 20 km downstream in 5 hours and returns against the stream in 15 hours, then the speed of the stream in km/hr is :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → $\frac{4}{3}$
B be the speed of the boat
S be the speed of the stream
Downstream Speed = B + S
$\frac{20}{B+S}=5$
$B+S=4$ ...(1)
Upstream Speed = B - S
$\frac{20}{B-S}=5$
$B-S=\frac{20}{15}=\frac{4}{3}$ ...(2)
Adding (1) and (2)
$(B+S)+(B-S)=4+\frac{4}{3}$
$2B=\frac{12+4}{3}=\frac{16}{3}$
$B=\frac{8}{3}$
Substituting B in (1)
$\frac{8}{3}+S=4$
$S=4-\frac{8}{3}=\frac{12-8}{3}=\frac{4}{3}$