On Don's facebook page, July 17, 2012: Hi Mr. C.! Thinking of you this morning as I started my day talking to Anna (7) about multiplying positive and negative numbers. We got out the chalkboard and I used postman stories to explain it to her! [Don learned it from Dr. Robert B. Davis in the '70s, Barbara learned it from Don in the '80s, and her girls learned it from Barbara in 2011(Cate) and 2012(Anna)- what a connection!]

There are 4 problems above:

Problem 1 (Monday) says the postman brings you 3 checks (^{+} 3) for $2 each (^{ +} 2) ; are you richer or poorer as a result? The checks are for your birthday, that adds $6 to your bank balance = (^{+} 6). So we write that as ^{+} 3 x ^{+} 2 = ^{+} 6 (you have $6 more)

Problem 2 (Tuesday) says the postman takes away 3 ( ^{-}3 ) (they really belong to the lady upstairs), checks for $2 each ( ^{+}2) ; are you richer or poorer as a result? you have $6 less than before he came. So we write that as ^{ -}3 x ^{+} 2 = ^{-}6

Problem 3 (Wednesday) says the postman brings you (^{+} 3) bills for $2 each ( ^{-}2 ); are you richer or poorer as a result? You have $6 less than before he came. So we write that as ^{ +}3 x ^{-}2 = ^{-}6.

Problem 4 (Thursday) says the postman takes away 3 ( ^{-}3 ) , bills for $2 each ( ^{-}2) (they really belong to the lady upstairs). So taking away the $6 in bills, adds $6 to your bank balance. So we write that as ^{-}3 x ^{-}2 =^{+}6.

"Mr. Cohen, I felt like I was channelling yesterday when Maggie and I got involved in figuring out how many pieces there were in the huge lego pyramid she had built. My favorite part was when she realized that there was a quicker but less interesting way to do the calculations, and she said, "Let's do it the longer way! It's more fun!"

I posted a photo of the pyramid and tagged you in it. I'm not sure if it's readable, but that white piece of paper says "10.404'

Donald Cohen: your pyramid is a marvel, Maggie! It looks like an Egyptian pyramid. I like the idea of doing something the longer way, but more fun in the process. Is the pyramid made by the squares of even numbers? Like 2^2=4, 4^2=16, 6^2=36?

Jennifer Olinger (a friend): Wow! That's impressive! Is that number (10,404) the number of Lego bricks she used?

Barbara: Not the number of bricks, the number of dots. A spontaneous unschooling math project.