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This shortcut technique is useful for the multiplication of nine series.
Let us see this shortcut with an example,
456 x 999
Step 1: Take the first value and subtract with 1.
456 – 1 = 455
Step 2: Subtract the first number from the base value. Here its 1000.
1000 – 456 = 544
Step 3: Combine the results of step 1 and step 2. So, the answer is 456 x 999 = 455544
Note: Use this shortcut when when both number have same number of digits.