I thought this was a great problem and wanted to share with you how I used it. I believe that the array model of multiplication and the partializing of a large array into smaller ones made up of multiples of tens is a very powerful model for kids learning about multiplication. For example, to solve the problem 24 X 8, you could subdivide the problem like this:
(10 X 8) + (10 X 8) + (5 X 8)
(20 X 8) + (5 X 8)
So, we did just this when figuring the area of Teresa's bathroom. It provided a great visual model for the kids to see how the sum of the parts equal the whole in multiplication. This is a natural strategy to use especially when finding the area of irregular polygons, which rooms so often are.