Multiplying single-digit numbers into double-digit numbers: The DS method

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  • #10755
    Areadien
    Participant
    • Topics: 4
    • Replies: 7

    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.

    #10777
    Abhishek R
    Keymaster
    • Topics: 0
    • Replies: 45

    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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