Final answer:
To find Johnny's average rate for completing his math work, divide the time taken by the number of problems in each instance.
Step-by-step explanation:
To find Johnny's average rate for completing his math work, we need to calculate the average time he took per math problem in both instances.
In the first case, Johnny took 15 minutes to complete 12 math problems. So, the average time per math problem is 15 minutes divided by 12, which is 1.25 minutes.
In the second case, Johnny took 34 minutes to complete 22 math problems. So, the average time per math problem is 34 minutes divided by 22, which is 1.55 minutes.
Therefore, Johnny's average rate for completing his math work is approximately between 1.25 and 1.55 minutes per problem.