Tom sent us a nice math trick to demystify. Let's put on our detective hats, click on the image below to see the trick and come back to the Puzzle Marathon to enjoy catching Robin in a fraud and understanding the simple solution.
You pick a two digit number. Let's use letters A and B to define digits in our number. Our number is AB. The value that our number represents is 10 x A + B.
For example, for A=1 and B=5, our number is 10 x 1 + 5 = 15.
Now, Regifting Robin instructs us to subtract both the first and second digit from our number: (10 x A + B) - A - B
Simplifing this we get: 10 x A - A + B - B = 9 x A
For A = 1 we get 9 x 1 = 9
For A = 2 we get 9 x 2 = 18
For A = 3 we get 9 x 3 = 27
Note that continuing with higher As we get all the multiples of 9.
Now we are ready to catch the Regifting Robin in a fraud!
Check Registing Robin's gift table. See what gift is in the cell#9, cell#18, cell#27, and all the other multiples of 9.
What? The same gift???!
No matter what numbers A and B we picked, if we did our math correctly, we get to a cell that is a multiple of 9 and all these cells contain the same gift. No wonder Robin can guess this gift!
Play again and you will see that a different gift is randomly selected but again all the cells that are multiples of 9 have the same gift.
What a fun mass dillusion! Subscribe to our weekly newsletter to get more of such fun tricks by email.