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Number Jumbler

First, we found out that the number with the symbol the number jumbler gest was a multiple of 9.

Then I tried all the sixty's (60,61,62,63,64,65,66,67,68,69,) and they all ended on the number 54.

How does this work?

6+9=15
69-15=54
6+8=14
68-14=54

You can see that the units (9,8) are going down so the number you are subtracting gets smaller and smaller (15,14) so the number will always be 54 for the sixties.

Another way you can explain this is when the subtrahend gets smaller (68,67,66) and you add the digits together each time the minuend will get smaller so the difference will stay the same until it gets to the fifty's (51,52,53,54,55,56,57,58,59,) so the difference is 45.