Question

How do you make a 10 to find 13-8

Answer 1

You can "make 10" out of either the positive number or the negative one.

13 - 8

= (10 +3) -8 = 10 +(3 -8) = 10 -5 = 5

= 13 -(10 -2) = (13 -10) +2 = 3 +2 = 5

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The latter approach would be used for computation using a soroban or abacus.