I went to Point B from point A at 3 km/h and returned to A from B at 6 km/h.
Find the speed of the average.
Answer
4 km/h
Solution
Average speed should be calculated by the formula of (total of advanced distance) / (total of the taken time).
First of all, because we do not know the distance between A and B, it makes decisions for oneself.
It to be easily calculated, it is assumed 6km in the lowest common multiple of 3 and 6.
The time it took to go is at 6km ÷ 3km / h = 2 hours, the time of return is 6km ÷ 6km / h = 1 hour.
Since the sum of the round-trip distance is 12km, average speed is 12km / (1 hour +2 hour) = 4km / h.