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Addition and subtraction to 800 again
Term 3
Build your own number families.
A warm up activity.
For each number below, choose 2 more to make a family. Write four number sentences (two + and two –) for each number family.
| + | + | – | – | |||
| 16 | 7 | 9 | 7 + 9 = 16 | 9 + 7 = 16 | 16 – 9 = 7 | 16 – 7 = 9 |
| 20 | ||||||
| 200 | ||||||
| 75 | ||||||
| 50 | ||||||
| 500 | ||||||
| 190 | ||||||
Find the missing doubles or halves
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|
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Halving to subtract.
If you know your halves and doubles, you can sometimes use them to add or subtract. Examples:
Now try these:
| 340 – 176 | 145 + 148 | 900 – 452 |
Study the ways.
256 children each get a Christmas present. Half get dolls and half get cars. How many get cars?
| Way 1 | Way 2 |
|
256 = 200 + 50 + 6
100 + 25 + 3 = 128
So 128 get cars. |
125 + 3 = 128
So 128 get cars. |
Half of 200 is 100
Solve the following on an extra piece of paper:
Use any of the above methods.
| 728 children each get a toy at the local restaurant. Half of them get building blocks. How many get building blocks? |
| 642 children each get a muffin. Half of them get chocolate chip muffins. How many get chocolate chip muffins? |
