Hello, hana_102!

This is a classic Trick Question . . .

If a cyclist travels at an average speed of 3m/s

and turns home at an average speed of 9m/s,

what is the average speed of the whole journey?

We will use: .

Suppose the distance (one way) is meters.

He cycled meters at 3 m/s.

. . This took him: . seconds.

He cycled back meters at 9 m/s.

. . This took him: . seconds.

The entire trip took: . seconds (Total time).

The total distance is: . meters.

Therefore, his average speed was: .