### Instruction: Jack drives at 40 mph for an hour, then at 50 mph for an hour.  What is his average speed?### Response: To find the average speed, I need to divide the total distance by the total time.
The total distance is the sum of the distances he traveled at each speed.
At 40 mph, he traveled 40 miles in one hour. At 50 mph, he traveled 50 miles in one hour.
So the total distance is 40 + 50 = 90 miles.
The total time is the sum of the times he spent at each speed.
He spent one hour at 40 mph and one hour at 50 mph, so the total time is 1 + 1 = 2 hours.