I'm having trouble with setting up problems that deal with two average formulas (An example would be the problem listed on Pg. 104 of Guide #4 [Word Translations]).

Problem: Sam earned a $2000 commission on a big sale, raising his avg. commission by $100. If Sam's new avg. commission is $900, how many sales has he made?

Even though the solution is listed in the guide, I can't quite grasp the concept correctly and consistently applying the steps on the In-Action problems (Namely, #8 & 10). Is there a video that teaches these types of questions specifically either by Ron or other instructors?

I tried searching for "Thursdays with Ron" videos by looking for ones that discussed about averages. But, they all deal with the topic of weighted averages, and I believe these problems are not considered as weighted averages since they're listed on a different section within the chapter.

If anyone can point me to the right video or tell me the name of these types of questions, it would be helpful.

Thank you!