## Thursday, April 23, 2015

I've been reading about these for so long and finally took the time to fit it in.  What fun!  The coolest thing is that my students really seemed to enjoy it and bought into it 100%!  I started off easy and kept it short the past two days.  Yesterday I gave them 56 + 7
Here are some of the responses I got.
63 because I know that 56 + 4 is 60 and 7-4 is 3 so 60+3 is 63
63 because I counted up from 56
63 because I added 6+7 is 13 then 10 plus 50 is 60 and add the 3 is 63
and one of my favorites:  Well, I know that 7x8 is 56 and 7x9 is 63 so the answer is 63 since I know the 7 times tables.

Today I gave them 16 x 25.  I thought I would get eye rolls and pencils (I told them to solve it with mental math.)  Again they all bought into it and I could see their brains all working on the problem (I think that is my favorite thing of all time.)
Here is what I got:
400 because 25 x 10 is 250 and 25 x 6 is 150 so 250 + 150 is 400
400 because 25 x 10 is 250, 250 divided by 2 is 125 and then add 25 to get 150.  150 + 250 is 400.
Then 16=4x4 and 25=5x5 so 4x5=20 and 4x5=20 and 20x20 =400

I really like the discussions that are starting to come from this.  Most students didn't really understand why the kid who divided 250 by 2 did that and I had him explain it further, then had other students summarize or restate what he said.  It was cool to see their light bulbs going off!

1. This is great, Robin! Here's my thinking on 16 x 25: I was counting money. I saw four piles of four quarters each, \$4 or 400.

Did you find any of the children unable to handle the 16 x 25? I wonder if it would work to have 2 or 3 problems and let students choose one or more to figure out? The discussions would probably not work as well for whole class. Just wondering if that would be a way to differentiate. What do you think?