1)A car travels from the place A to B with a speed of [tex]V_{1}[/tex]. During its return journey from B to A its speed is [tex]V_{2}[/tex]. Then the average speed in complete journey is...(please I need the explanation).

2) If a car covers first 2/5th of the total distance with a speed [tex]V_{1}[/tex] and remaining 3/5th of the total distance with a speed of [tex]V_{2}[/tex], then its averag speed is...(Explain me)

3)A body has a speed of V, 2V and 3V in the first 1/3 distance, second 1/3 distance and the remaining of the total distance respectively. then the average speed is...
(Explanation is needed)...