Final answer:
To find the total number of problems on Christopher's math homework, divide the number of problems he has left by the percentage of homework he completed. It was found that there were 20 problems on Christopher's math homework.
Step-by-step explanation:
To find the total number of problems on Christopher's math homework, we need to divide the number of problems he has left by the percentage of homework he completed.
First, we find the percentage of homework he completed: 100% - 65% = 35%
Then, we set up a proportion: 35/100 = 7/x
Cross multiplying, we get 35x = 700, and solving for x, we find that x = 20.
Therefore, there were 20 problems on Christopher's math homework.