Addition: putting things together
๐ In short
If you have 3 balloons and your friend gives you 2, how many do you have now? 5! That's addition: we put two groups together to find out how many we have. We write it with the + sign, read โplusโ, and the answer is called the โsumโ.
๐คฉ Did you know?
- The + sign appeared in books more than 500 years ago and comes from a Latin word meaning โandโ.
- The numbers from 1 to 100 add up to 5050.
- Any number + 0 = the same number.
- A computer does more than a billion additions a second.
๐ Find out more
๐ Order doesn't matter
3 + 5 = 5 + 3 = 8. When we add two numbers we can swap them and the sum doesn't change. So we always start with the bigger number and count on: 2 + 9? We start at 9 and say: 10, 11.
๐ Friends of ten
1 and 9, 2 and 8, 3 and 7, 4 and 6, 5 and 5: these are โfriends of tenโ, because each pair adds up to 10. If you know them by heart, adding gets easy: 7 + 5 = 7 + 3 + 2 = 10 + 2 = 12.
๐ก Adding by place
To add two big numbers we add each place on its own: ones with ones, tens with tens. 34 + 25: ones 4 + 5 = 9, tens 30 + 20 = 50, so the sum is 59.
๐ฏ Carrying
If the ones add up to more than 9, we carry the ten to the tens place. 38 + 25: ones 8 + 5 = 13, write 3 and carry 1 to the tens: 3 + 2 + 1 = 6. The sum is 63.
๐ See it in a picture
๐งฎ Worked examples
- 8 + 6 = 8 + 2 + 4 = 14Make 10 first, then add the rest.
- 45 + 32 = 7740 + 30 = 70, and 5 + 2 = 7.
- 27 + 18 = 457 + 8 = 15: write 5 and carry 1, then 2 + 1 + 1 = 4.
๐ Key words
- Addition
- Putting two or more numbers together to find the total
- Sum
- The answer to an addition
- Carrying
- Moving a ten from the ones place to the tens place
๐งช Try it at home
Play with two dice with someone in your family: roll the dice and add the two numbers quickly. Whoever says the sum first gets a point. Which sum comes up most often?
๐งฉ Test yourself
1 What is 7 + 8?
2 Which pair are โfriends of tenโ?
3 What is 36 + 47?