you drive in a straight line at 20.0m/s for 10.0 min, then 30.0m/s for another 10.0 min. Find the average speed.

Answer is 25 m/s.

Explanation;

Step 1 : Convert the units into same unit.

Here speeds are given in m/s while the time is in minutes. So, let's convert minutes into seconds.

1 min = 60 s

Then,

10 minutes = 10 x 60 s = 600 s

Step 2 : Find the total distance that you have travelled.

To find that you need to first find distances separately.

We know the formula, s = vt, where s is the distance, v is the speed or velocity and t is the time.

First you have travelled 10 minutes (600 s) at 20.0 m/s.

Then distance, s = 20.0 m/s x 600 s = 12 000 m

Secondly you have travelled again 10 minutes at 30.0 m/s

Then distance = 30.0 m/s x 600 s = 18 000 m

Then, the total distance = 12 000 m + 18 000 m = 30 000 m

Step 3 : Find the total time taken to travel.

Total time = 600 s + 600 s = 1200 s

Step 4 : Calculate the average speed.

Average speed = total distance / total time

= 30 000 m / 1200 s

= 25 m/s