Question

A swimmer can swim 10 km in 2 hours when swimming along the flow of a river. While swimming against the flow, she takes 5 hours for the same distance. Her speed in still water (in km/h) is ________.

Answer 1

Let her speed = x km/hr

She is travelling 10 km in 2 hrs so (along with flow)

\(\therefore Speed = \frac{{distance}}{{time}}\)

\(\therefore Speed = \frac{{10\;km}}{{2\;hr}}\)

Speed = 5 km/hr (along with flow)    --- (1)

She takes 5 hours for same distance when swimming against the flow

\(\therefore Speed = \frac{{distance}}{{time}}\)

\(Speed = \frac{{10\;km}}{{5\;hr}}\)

Speed = 2 km/hr (against the flow)      --- (2)

Now from eqⁿ (1) & (2) we get

x km/hr + (flow of river) km/r = 5 km/hr ----------(3)

x km/hr – (flow of river) km/hr = 2 km/hr----------(4)

Adding (3) & (4)

2x km/hr = 7 km/hr

∴ x = 3.5 km/hr