Regifting Math Puzzle ???

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Can anyone figure out how this is done ??? I can’t see any mathmatical connection to the solution.

http://www.regiftable.com/RegiftingRobinPopUp.html

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There are a limited number of possible answers on the board. If you said 83, then 83-8-3=72. 99-9-9=81. Both of these answers and the rest all have the same answer on the board. The possible answers are :SPOILER: 81,72,63,54,45,36,27,18,9

The logic is that since we are starting with a 2 digit number, subtracting the 1 spot number brings you to the rounded to 10 spot and then subtracting the 10 spot number brings you down to the 1 spot. I know, lousy explaination, but there you go.

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Can anyone figure out how this is done ??? I can’t see any mathmatical connection to the solution.

http://www.regiftable.com/RegiftingRobinPopUp.html

Any 2 digit number can be represented as 10A + B where A is 1 -> 9 and B is 0 -> 9.
If you subtract both digits from this, you always end up with a multiple of 9:

10A + B – A – B = 9A

You’ll note that all the prizes for multiples of 9 are the same! Not so “gifted” after all!

Alan

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Thanks guys !!!

One can always count on the Lounge Brain Trust when an intelligent solution is required.

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Well, it didn’t get some of my numbers correct – but that was mainly because I got my maths wrong

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