Neat game to teach addition and subtraction

We agree on difference of 2.

Kate: (hides a certain number of fingers)
Me: It’s less than how many fingers?
Kate: 6
Me: you’ve got 4 fingers!
Kate: yup

Me: ( I hide my fingers )
Kate: It’s more than how many fingers?
Me: 7
Kate: You’ve got 9 fingers!
Me: Yeah!

As they get better, increase the difference.
We can play this for 30 mintues. Good way to kill time on BART.