erhm, did you not notice the top solution? ;)

I know this is 17 months old, but thank you for this! I actually didnt know you could remove the else and just add another return for "Odd".

The Func part is a delegate and the (x) => ... part is a lambda expresion but I don't know the advantage of using them here.

As g964 says in your post below, you are missing a using statement - add using System; above everything else in your solution. Math is short for System.Math in C#, but you need the initial using statement for this to work.

Alternatively you could replace Math with System.Math everywhere in your solution.

Please before posting issues look at the top of the page: 4975 people passed the C# kata so you could have seen that it's not an issue of the kata but a problem of your code. To use Math.Pow you need "using System;".

In that case a == b, so it's indifferent which of them is returned. In the current case b will be returned, but the condition could be a >= b as well in which case a would be returned when the are equal.

then either one is ok