Vn116.1 Transferring a Good Trick 1/3/78

Miriam, not imagining yet that she will one way or another make
a living, sees her best hope of getting a lot of money as inheriting my
money. Thus my impending demise is a subject on her mind and one that
involves her in computations. At lunch today:


Daddy, if you die in another 37 years — no, if you die in another 30 years you will be 67.

Right. But suppose I live those 37 years. How old will I be then?

(After a short pause, wherein she raised and lowered a few fingers) 74.

That’s absolutely correct. How did you ever figure that out?

I know a good trick. See, you have the 67. And you know the other 7?

(Nodding assent here)

Well, that’s like a 3 and a 4. So I took the 3 with the 67 and that’s 70 and then the 4 left over made 74.

That’s beautiful, sweetheart.

This is the first time I have witnessed Miriam doing a sum with
a decade crossing without the use of a counting-up procedure to sum the
secondary units addend with the intermediate result.

What I find most striking in this decomposition of a single
units digit is that the trick (though similar to her reduction to nines
technique for carrying) was first explicitly applied as a procedure for
mental addition in decadal arithmetic (cf. Vignette 105, Decadal Compu-
tation). Thus here we witness a procedure developed for summing large
numbers being retrofitted to addition of small numbers, and in that
microworld supplanting (in this case) the serial counting-up procedure.

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