A boat racer can row 21$\frac{3}{2}$ km/h in still water. If the speed of river is 12.5 km/hr, it takes him 40 minutes to row to a place and back, how far off is the place (consider up to two decimals)?

5$\frac{5}{27}$ km

According to the question,

Let the distance be x, then,

Upstream speed

=  21$\frac{3}{2}$ km/h - 12.5 km/h

= 22.5 - 12.5  = 10 km/h

Downstream speed 

= 22.5 km/h + 12.5 km/h

= 35 km/h

According to the question,

\(\frac{x}{10}\)  + \(\frac{x}{35}\) = \(\frac{40}{60}\)

= x(\(\frac{1}{10}\) + \(\frac{1}{35}\)) = \(\frac{2}{3}\)

= x(\(\frac{45}{350}\)) = \(\frac{2}{5}\)

= x = 2 ×  \(\frac{70}{3}\) × 9

= x = 5$\frac{5}{27}$ km