You drive in a straight line at 20.0 m/s for 10.0 min, then at 34.0 m/s for another 10.0 min. What is the average speed?

To answer this question, you need to count the total distance traveled. The calculation would be:

Total distance = v1 * t1 + v2*t2 = 20m/s * 10 min * 60 sec/min + 34 m/s * 10 min * 60 sec/min = 12000m+20400m = 32400m.

Then you need to divide the distance with the total time to find the average speed.

It would be: 32400m / (10min+10min) = 32400m/20min * 1 min/60sec = 27m/s