Math Trick

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.

Enjoy!

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13 comments

Mi 5 years ago

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


douglas 6 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???


Tom 6 years ago

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


hsfudhk 7 years ago

this is very cheap trick


arrah 7 years ago

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


Chuck profile image

Chuck 8 years ago from Tucson, Arizona Author

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


micheal 8 years ago

i cant understand your tricks.it is local


mathman 8 years ago

its not Interesting

its very easy to understand how

its like that i say 2+2=4


BonG 9 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


Renganathan 9 years ago

Very Interesting


Alex 9 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 9 years ago from Tucson, Arizona Author

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.

Chuck


Lee 9 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.

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