A number and its reverse
Level
1
Supposing I add a number XY to its reverse YX. The resultant number is always divisible by
11
X
9
Y
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1 solution
XY can be written as 10X + Y. The opposite of this number YX can be written as 10Y + X. Adding these two yields the new number 11X + 11Y OR 11(X+Y), which is most certainly divisible by 11.