 Now you know how to add numbers. How about if there are 3 add-ins? How are you going to do it? Take a look at this sample. How do we find the sum of 4 plus 3 plus 2? So first we have to add 4 and 3. 4 plus 3 equals 7. Then we add 2. 7 plus 2 equals 9. 4 plus 3 plus 2 equals 9. Let's have another example. How do you find the sum of 5 plus 3 plus 4? First we add 5 and 3. 5 plus 3 equals 8. 8 plus 4 equals 12. 5 plus 3 plus 4 equals 12. That is one way to add to find the sum of 3 add-ins. To add the first 2 add-ins, then add the third add-in, then you find the sum. Here is another way. To find the sum, first let's find the pair with the sum of 10. In this case, 6 and 4. 6 and 4 is 10. 10 plus 5 equals 15. 6 plus 4 plus 5 equals 15. Let's have another example. First let's find the pair with sum of 10. In this case, 1 and 9. 1 plus 9 equals 10. 10 plus 7 equals 17. 1 plus 7 plus 9 equals 17. So you see that if you know how to find the pair with sum of 10, you can easily do the addition operation to find sum with 3 add-ins. Do the activities in your book now. Practice finding the sum of 3 add-ins. Practice makes perfect. Good luck.