Why don't these methods work?

Question

"int[ ] arr = { 2, 4, 7, 1};
Console.WriteLine(arr.Max());
//Outputs 7

Console.WriteLine(arr.Min());
//Outputs 1

Console.WriteLine(arr.Sum());
//Outputs 14"

These are from the C# SoloLearn tutorial and in the CodePlayground they work. Yet in my IDE throws an error for all three of them.

Answer 1

Min, Max and Sum require Linq extension.
Try to add this
using System.Linq;

Answer 2

I use SharpDelevop. Thanks Atomx!

Answer 3

what kind of error? Are you using Visual Studio?