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Challenge 15 Answer


Check Filling Error

On the check it was written:… xxxABx
But the correct would be:… xxxBAx

That is, in the tens of check was written B (that's what we want to find).

Therefore the person paid R $ 270,00 more, so doing the subtraction the result will be 270:

… XxxABx
… XxxBAx
----------------
… 000270

Therefore we must have AB - BA = 27

The exercise says that A and B are with each other as 1 is for 2. Hence we know that A is twice B, ie: A = 2B.

Knowing this, there are 4 possible values ​​for A and B:

B = 1 and A = 2 => 21-12 = 9 => this can't be (since AB-BA = 27)
B = 2 and A = 4 => 42-24 = 18 => this can't be (since AB-BA = 27)
B = 3 and A = 6 => 63-36 = 27 => these are the values ​​(because AB-BA = 27)
B = 4 and A = 8 => 84-48 = 36 => this can't be (since AB-BA = 27)

Therefore the values ​​are A = 6 and B = 3.

Answer: The digit written on the check in the tens was 3.

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