# \( (XY+ YX )\) % 7?

**Number Theory**Level 3

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.