I am a huge fan of number talks and use Sherry Parrish’s book at least two to three times a week to conduct a number talk with my students.  Sometimes I pose just one problem for students to solve mentally and discuss strategies while making connections between them or I do a string of problems targeting a specific strategy.  Recently, I have been focusing on partial products and using friendly numbers as strategies to multiply. I noticed that as the string went along, they wanted to try and predict what the final problem (or “the hard problem” as my students would say) in the string would be. I started taking a few predictions each time and the conversation was really intriguing to me.

For example, the other day, the string was:

5 x 10

5 x 50

10 x 50

15 x 50

15 x 49

As they predicted the final problem, they actually made a more difficult prediction than the ending problem, 15 x 49. They predicted problems such as 15 x 47, 30 x 51 and 15 x 52.  Their reasonings were targeting the strategy of using friendly numbers without me having to outwardly say it.

So I thought it would be interesting (and fun) to go in the opposite direction and give them the last problem of a string  to see if they could develop the string of three problems that would come before it.  I gave them “36 x 19” and they ran with it.  Here are some ideas i captured from the journals:

This is a great formative assessment for me to see their thought process through our multiplication problems. Definitely adding it to my list of favorite activities!

~Kristin

Number Talks by Sherry Parrish: http://store.mathsolutions.com/product-info.php?Number-Talks-pid270.html