Returning to a challenging counting problem

[I didn’t have a lot of time to write this one up, but wanted to get it published anyway. Sorry to be so brief.]

A few weeks ago we looked at a pretty challenging counting problem:

How many 3 digits numbers have their digits in increasing order?

Today we revisited the idea in this problem by looking at a slightly different question:

How many three digit numbers have their digits in descending order?

The boys had a hard time seeing the way to approach this problem with choosing numbers – our talk through that concept is in the last two videos. BUT . . . they did a super job of approaching the problem through case by case counting, even finding a nice pattern in the numbers! That work is in the first two videos.