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I think you already know how important it is to know your tables well. In this learning unit it will help you to multiply quickly and correctly. Let us see how well you know your tables.
1. Take the fruit-shaped sweets containing the correct answers out of the jar. Colour them in neatly and then write down the letter of the alphabet written on it. Use these letters to complete the sentence:
_____________ is a shorter way of doing repeated addition.
1.1 5 × 4
1.2 2 × 3
1.3 7 × 7
1.4 7 × 4
1.5 5 × 5
1.6 7 × 3
1.7 6 × 4
1.8 9 × 2
1.9 9 × 7
1.10 9 × 9
1.11 7 × 6
1.12 3 × 5
1.13 8 × 8
1.14 12 × 4
1.15 6 × 12
1.16 9 × 12
1.17 6 × 6
1. Now that you know exactly what factors are, you are probably able to see their important function in multiplication. Factors also help us to test our answers when we multiply. Yes, you are right! We use them when we divide in order to test whether we have multiplied correctly. Now see how many pairs of factors you can write down for the following numbers.
| a) 24 = ............ × ............ | b) 36 = ............ × ............ |
| = ............ × ............ | = ............ × ............ |
| = ............ × ............ | = ............ × ............ |
| = ............ × ............ | = ............ × ............ |
| = ............ × ............ |
2. Let us do some more exercises, using factors. Look at the products (numbers) and then write down suitable factors for them. The first one has been done for you.
| 42 | 45 | 63 | 54 | 64 |
| 7 × 6 | ...................... | ...................... | ...................... | .................................... |
| 72 | 108 | 48 | 88 | 96 |
| ...................... | ...................... | ...................... | ...................... | .................................... |
DO YOU STILL REMEMBER?
When you multiply any number by 0 , the answer is always 0 . (0 × 6 = 0)
Any number multiplied by 1 , is that number. (9 × 1 = 9)
Now the factors are supplied to you. All you have to do in your first mental arithmetic test is to complete the multiplication block by writing down the missing answers only. Easy, isn’t it?
| X | 4 | 5 | 6 | 7 | 8 | 9 | 12 |
| 5 | 20 | ............ | 30 | ............ | 40 | ............ | 60 |
| 6 | ............ | 30 | 36 | 42 | ............ | 54 | ............ |
| 7 | 28 | ............ | 42 | ............ | 56 | ............ | 84 |
| 8 | ............ | 40 | ............ | 56 | ............ | 72 | ............ |
| 9 | ............ | ............ | 54 | ............ | 72 | ............ | 108 |
| 2 | 48 | 60 | ............ | 84 | ............ | 108 | ............ |
By doubling numbers we can find the answer to a multiplication sum much more easily. Here we can learn from the Egyptians. Work with a friend and see whether you are able to find out how this calculation was done.
28 × 324
| 1 × 324: | 324 | (1 × 324) |
| Double 324: | 648 | (2 × 324) |
| Double l 648: | 1 296 | (4 × 324) |
| Double 1 296: | 2 592 | (8 × 324) |
| Double 2 592: | 5 184 | (16 × 324) |
| Thus: 28 × 324 = | 9 072 |
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