Decimal Multiplication

This is a quick lunchtime post, so not much time to reflect or analyze, but wanted to throw it out there..

We did a Decimal number talk today and ended with the problem 5 x 4.6

I had students double half, use partial products, and use friendly numbers. (Incorrect answers were also written in case you are wondering about the 21.6 and 35…we looked for errors also)


Then one student said that she bumped the 5 up to 6 and did 6 x 4 because she knew that faster, however she couldn’t figure out how to adjust her answer based on what she did. We had already had someone explain how they adjusted from 5 x 5, but this was not the same. She knew that she needed to subtract 1 (because we had already established 23 was correct) but where was that 1 coming from?

I sent them back to their groups to talk about it.

One group had this idea…


I asked them if it always worked so they tried some more problems at the bottom that did not. They tried some more….


They found one that worked….hehe..


The class had to leave for lunch, but I will keep you posted what they come up with…


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