Question : I have to create 5 threads where each thread has to perform the addition operation.

* Thread1 - Add 1 to 10
* Thread2 - Add 1 to 50
* Thread3 - Add 5 to 15
* Thread4 - Add 10 to 20
* Thread5 - Add 15 to 20

What is the best way to accomplish this? Also, I need 1 sec time delay between each addition operation. I have written this code: 
My output is wrong and changing every time. I know problem is with synchronized but not able solve.

```
class adding implements Runnable{
    int a,b; 
    public adding(int a, int b){
        this.a = a;
        this.b = b;
    }
    public void run() {
        add(a,b);
    }
    public void add(int a, int b){
        int sum=0;
        synchronized (this) {
            for(int i=a;i<=b;i++){
                sum = sum+ a;
            }
            System.out.println("Sum of "+a+" to "+ b+" numbers = "+sum);    
        }
    }
}

public class addnumbersusing5threads {
    public static void main(String[] args) {
        Thread t1 = new Thread(new adding(1,10));
        Thread t2 = new Thread(new adding(1,50));
        Thread t3 = new Thread(new adding(5,15));
        Thread t4 = new Thread(new adding(10,20));
        Thread t5 = new Thread(new adding(15,20));
        t1.start();
        t2.start();
        t3.start();
        t4.start();
        t5.start();
    }
}

```

Output:

```
Sum of 1 to 10 numbers = 10  
Sum of 1 to 50 numbers = 50 
Sum of 5 to 15 numbers = 55 
Sum of 10 to 20 numbers = 110 
Sum of 15 to 20 numbers = 90 

```