how to call multiple method asyncronsly on button click

you can work around ThreadPool[^]

for example

first of all you need to create static method/function which is actually called in threading, like this:-

// This thread procedure performs the task.
    public static void ThreadProc(Object stateInfo) {
        Console.WriteLine("Hello from the thread pool.");
    }

and call it like this...

ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc));

for passing value to your method you can do something like this:-

public class ThreadPara{
   public int a{get;set;}
   public int b{get;set;}
}

public static void ThreadSum(Object stateInfo) {
    ThreadPara data = stateInfo as ThreadPara;
    int sum = data.a + data.b;
    Console.WriteLine("Sum is :" + sum);
}
public static void ThreadMul(Object stateInfo) {
    ThreadPara data = stateInfo as ThreadPara;
    int mul = data.a * data.b;
    Console.WriteLine("Mul is :" + mul);
}

and call it in button click like this..

protected void btn1_Click(object sender, EventArgs e)
{
    ThreadPara data = new ThreadPara();
    data.a = 10;
    data.b = 20;
    ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadSum),data);
    ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadMul),data);
}