Cannot Convert from Method Group to Object - C#

You need select.Average() (with the parens).

The Missing Parenthesis () is the reason for your error.It should be Average()

without a Parenthesis,it is understood as a method group.The average method could have multiple overloads and it is unclear which specific overloaded method needs to be invoked.But when you mention the parenthesis it makes the intention clearer and the method gets called.