The nines complement is the number needed to make a single digit add up to 9. This technique is a building block for use in other tricks.
Step 1
Subtract the number that you are finding the 9’s complement of from 9.
9 - 7 = 2
Step 2
The result of step 1 is the 9’s complement.
2 is the 9’s complement of 7.
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This technique can be used with any large number. Simply take the 9’s complement of each digit to find the 9’s complement of the entire number.
9’s complement of 6347?
= 3652
Step 1
Subtract each digit in the number from 9.
9 - 6 = 3
9 - 3 = 6
9 - 4 = 5
9 - 7 = 2
= 3652