2
Adding by place value
Discover Mathematics P2: Term 1, Lessons 31–40
GoalAdd two-digit numbers by adding the tens and then the ones.
New words
add · to put numbers togetherplace value · what a digit is worth in its placeestimate · to find an answer that is close, without working it out exactly
Explanation
To add two-digit numbers, break each number into tens and ones. Add the tens together, add the ones together, then put the answers together. For 24 + 13: tens 20 + 10 = 30, ones 4 + 3 = 7, and 30 + 7 = 37. You can also write the numbers in a column, with tens under tens and ones under ones.
| Number | Tens | Ones |
|---|---|---|
| 24 | 20 | 4 |
| 13 | 10 | 3 |
| 37 | 30 | 7 |
Worked examples
24 + 13: 20 + 10 = 30 and 4 + 3 = 7. 30 + 7 = 37.
41 + 36: tens 40 + 30 = 70, ones 1 + 6 = 7. 41 + 36 = 77.
Marwan has 52 stickers and gets 27 more. 50 + 20 = 70 and 2 + 7 = 9, so he has 79 stickers.
Class activity
Shell shop. Count out small things, such as 32 beans in one bowl and 25 in another. Add the tens, then the ones, and tell the total. Count together to check.
Practice
1
What is 32 + 25?
57
2
What is 61 + 28?
89
3
What is 40 + 39?
79
4
What is 55 + 43?
98
5
Seif collected 34 shells and Nour collected 45. How many shells did they collect?
79 (30 + 40 = 70 and 4 + 5 = 9)