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)?
Answer & explanation
Correct answer: option 1
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