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:
| Miriam | Daddy, if you die in another 37 years — no, if you die in another 30 years you will be 67. |
| Bob | Right. But suppose I live those 37 years. How old will I be then? |
| Miriam | (After a short pause, wherein she raised and lowered a few fingers) 74. |
| Bob | That’s absolutely correct. How did you ever figure that out? |
| Miriam | I know a good trick. See, you have the 67. And you know the other 7? |
| Bob | (Nodding assent here) |
| Miriam | 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. |
| Bob | That’s beautiful, sweetheart. |
Relevance
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.
