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Math Trick

Updated on May 5, 2011

A Brain Teaser

Here is a trick I ran across and found interesting.

Think of a 3-digit number where the difference between the first and last digit is at least 2 (for example, 124 works, 122 does not).

Reverse the number and subtract the smaller from the larger.

Reverse this new number, and add it back to the result of Step obtained above.

70% of the time you will get 1089.

I Tried this 10 Times and Got 1089 Each Time

Give this a Try Yourself

As you can see from my numbers above, I tried this with ten different numbers and came up with 1089 as the result each time.

Try this yourself and let me know if you can find any numbers which are in the 30% that do not result in 1089.



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    • profile image

      Mi 6 years ago

      You are wrong. try this number 569. The result can't be 1089. Good try anyway! :)

    • profile image

      douglas 8 years ago

      at 12 noon the principal sent home 1/3 of the student plus 6.

      at 1pm she sent home 1/4.

      at 2pm she sent home the rest which was 21 how many did she start with???

    • profile image

      Tom 8 years ago

      I have known of this "trick" for over 20 years, but can't find anyone who can explain algabraicly why it works!

    • profile image

      hsfudhk 8 years ago

      this is very cheap trick

    • profile image

      arrah 8 years ago

      nicE tricks....hehehe...Good Job...tnx

    • Chuck profile image

      Chuck Nugent 9 years ago from Tucson, Arizona

      michael - I think that the word you want is "loco" not "local"

    • profile image

      micheal 9 years ago

      i cant understand your is local

    • profile image

      mathman 9 years ago

      its not Interesting

      its very easy to understand how

      its like that i say 2+2=4

    • profile image

      BonG 10 years ago

      this one is easier....

      find a 3 digit number then reverse it.ex.. 256->652...subtract to get 396 then reverse it again(693) then add...answer 1089....try it

    • profile image

      Renganathan 10 years ago

      Very Interesting

    • profile image

      Alex 10 years ago

      Hmm.. Is it not interesting that the number in Step 4 & 5 always turns out to be a 2-digit multiple of 9, with 9 separating the two digits?

      18 --> 198

      27 --> 297

      36 --> 396

      The middle number is always 9, while the outer two numbers make up a multiple of 9! Just thought I might point that out.

    • Chuck profile image

      Chuck Nugent 10 years ago from Tucson, Arizona

      Lee, thanks for the comment. I came across this in one of the email newsletters that I subscribe to and they claimed that 1089 was the result 70% of the time. I tried the ten different numbers and came up with 1089 each time. I considered, but did not take the time, to set up a spreadsheet to test each number between 99 and 999. I also did not test the claim in the newsletter that the difference between the first and third digit of the number has to be greater than two. If I am reading your comment correctly, it appears that this is not true either and the 1089 result occurs when you do the trick with every number between 99 and 999. Thanks again for the comment and hope you enjoyed the trick.


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      Lee 10 years ago

      I checked this with a spreadsheet. If you consider the reverse of 99 to be 990, and the reverse of 100 to be 1, then every 3 digit number will yield 1089 unless the first and last digits are identical, in which case the result is 0. I'm not sure where the 70% comes from.