An aeroplane flies from place A to place B at the speed of 500 km/hr. On the return journey, its speed is 700 km/hr. The average speed of the aeroplane for the entire journey is ?
Correct Answer: $$583\frac{1}{3}{\text{ km/hr}}$$
Average speed :
$$\eqalign{ & {\text{ = }}\left( {\frac{{2 \times 500 \times 700}}{{500 + 700}}} \right){\text{ km/hr}} \cr & {\text{ = }}\left( {\frac{{1750}}{3}} \right){\text{ km/hr}} \cr & {\text{ = }}583\frac{1}{3}{\text{ km/hr}} \cr} $$
$$\eqalign{ & {\text{ = }}\left( {\frac{{2 \times 500 \times 700}}{{500 + 700}}} \right){\text{ km/hr}} \cr & {\text{ = }}\left( {\frac{{1750}}{3}} \right){\text{ km/hr}} \cr & {\text{ = }}583\frac{1}{3}{\text{ km/hr}} \cr} $$