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So I figured out a way to verify the DS method of multiplying single-digit numbers into double-digit numbers. You just subtract 9 from the multiplicand and multiplier as necessary, multiply the differences together, and do DS on the result. So, for example, let’s take 5 * 3 = 15.
5 – 9 = -4. 3 – 9 = -6. -4 * -6 = 24. 2 + 4 = 6. 1 + 5 = 6. So 5 * 3 =1 5.
I haven’t tried this with other single-digit numbers, but I figured I’d share this manipulation of the DS method for this case.
Ah very useful indeed. If you notice your steps, you are converting the single digit multiplication problem into another multiplication problem 4 x 6 = 24. I would therefore recommend learning the single digit multiplication table by heart.
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