Question

a cyclist goes uptill at a speed of 5 km/h . if the uphill and down hill at a speed of 40 km/h journeys involve the same distance , what is his average speed during his whole journey .

Answer 1

$V= \frac{2}{ \frac{1}{5} + \frac{1}{40} } \\ \\ \Rightarrow V= \frac{2}{ \frac{8+1}{40}} \\ \\ \Rightarrow V= \frac{2 \times 40}{9} \\ \\ \Rightarrow V= \frac{80}{9}\ km/h$