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.
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.