Multiply by 9999 trick

Multiply by 9999 trick

Here is a nice trick to multiply a 4 digit number by 9999.

For instance, lets try multiplying 1729 by 9999.

First, we reduce 1729 by 1.

1729-1=1728

Then, we subtract each of the above digits from 9 to get 8271.

(9-1=8, 9-7=2, 9-2=7, 9-8=1)

In conclusion, 9999 x 1729=1728,8271.

Impressive isn’t it?

This trick works for many 9s too, for example multiplying by 99999999.

To multiply 9999 with a number with less digits, for instance, 12, simply pad zeroes in front of the number, to become 0012.

Then, using the above method, 9999 x 0012 = 0011,9988=119988.

Secrets of Mental Math: The Mathemagician’s Guide to Lightning Calculation and Amazing Math Tricks

Author: mathtuition88

http://mathtuition88.com

2 thoughts on “Multiply by 9999 trick”

  1. You can do the same with Vedic Math:

    1729 -> – 8271 (all -9, last -10)
    9999 -> – 1 (all -9, last -10)
    =============
    -8271 x (-1) = 8271 (x vertically)
    1729 + (-1) = 1728 (+ crossed)

    Answer = 1728,8271 [QED]

    Like

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