The Enemy of My Enemy – Steven Strogatz on Math

It’s traditional to teach kids subtraction right after addition. That makes sense — the same facts about numbers get used in both, though in reverse.  And the black art of “borrowing,” so crucial to successful subtraction, is only a little more baroque than that of “carrying,” its counterpart for addition.  If you can cope with calculating 23 + 9, you’ll be ready for 23 – 9 soon enough.

At a deeper level, however, subtraction raises a much more disturbing issue, one that never arises with addition. Subtraction can generate negative numbers

via The Enemy of My Enemy – Opinionator Blog – NYTimes.com.

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