\( (XY+ YX )\) % 7?
If the number 16 is added to its reverse, \(16+ 61= 77 \).
The sum is 77 which is divisible by 7.
But you will not find many numbers have this property.
For example \( 15 + 51 = 66\), which is not divisible by 7.
How many two digit-number has this properties?
Assume that \(05 \) is not a two-digit number.