At lunch, I inquired of Miriam how she used to add on her fingers
numbers like 2 plus 7. After saying ‘9’ and my refusing that answer,
she counted up, i.e. Miriam said ‘7’ then lifting her pinky and fourth
finger on the right hand, ‘8, 9.’

I again rejected the answer: “Try hard to remember when you couldn’t
do any sums greater than 10, how did you add 2 plus 7 then?” Miriam
counted from 1 to 7 using her right hand and the pinky and fourth finger
of her left hand; she then raised her thumb and index finger, saying
‘1, 2’ thus leaving her middle finger unused.

Miriam complained that she no longer enjoyed doing such easy sums,
so I asked her to add 37 and 12. She looked shocked — then said ’49.’
When asked, she explained: “I knew it had to be more than 40 ’cause it’s
like 30 plus 10, so I said ’47,’ then ‘8, 9’ because of the 2 left over.”
(Miriam counted upon her hand for the last 2).

Relevance
This vignette confirms a speculation (cf. How Miriam Learned to
Add) that Miriam’s early use of commutativity is an artifact of her
finger counting procedure in that selecting the larger of two addends
to first represent is less confusing where the sum approaches 10.