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The ideas in this multiplication lesson are taken from Math Mammoth Multiplication 2 book. Only a few examples of each problem type are shown; you should make more problems of each kind for the student. Multiplying in parts - a preparation for multiplying in columns
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We know that 5 × 12 = 60 from studying the multiplication
tables. Look at
the pictures
and see how the same problem can be solved very easily!
Each 12 is 10 + 2. We multiply the tens and ones separately and then add: 5 × 12 = 5 × 10 + 5 × 2 = 50 + 10 = 60 |
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Each 27 is 20 + 7. Multiply the tens and ones separately and then add: 3 × 27 = 3 × 20 + 3 × 7 = 60 + 21 = 81 |
Examples:
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6 × 18 = 6 × (10 + 8).
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7 × 32 = 7 × (30 + 2).
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The video below also explains this same idea: first students are taught to multiply two- or three-digit numbers in parts (such as multiplying 3 × 89 as 3 × 80 and 3 × 9, and adding those) as a preparation for learning the usual multiplication algorithm.
Example problems
1. Draw ten-sticks and one-dots to illustrate the numbers. Then use the distributive property to multiply.
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5 × 23
5 × 23 = 100 + 15 = 115 | ||||||||||||
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3 × 65
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2 × 58
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4 × 26
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2. Break the second number (factor) into tens and ones. Multiply in parts (tens and ones separately), and add.
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5 × 17 = 5 × (10 + 7).
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8 × 41 = 8 × (__ + _).
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4 × 17 = 4 × (__ + _).
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6 × 53 = 6 × (__ + _).
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3. Break the second number (factor) into tens and ones. Multiply separately, and add.
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a.
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c.
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e.
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4. Now break the second number (factor) into hundreds, tens and ones. Multiply in parts (hundreds, tens, and ones separately), and add.
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a. 5 × 123
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b. 8 × 115
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g. 5 × 194
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h. 7 × 109
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5. Write a mathematical sentence(s) for the problems. Multiply using the principle above (distributive property).
| a) Mom bought five sheets and blanket. The sheets cost $15
each, and the blanket cost $7. How much was her total bill?
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| d) A haircut costs 13 dollars. But, you can buy a discount
ticket for $65 that gives you six haircuts. How much money do you
save by buying the discount ticket?
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6. Continue the patterns.
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a. 3 × 80 = 4 × 80 = 5 × 80 =
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d. 6 × 50 = 6 × 60 = 6 × 70 =
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7. Continue the patterns. Think back to multiplication.
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a. 650 × 10 = 660 × 10 = 670 × 10 = 680 × 10 =
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d. 180 × 3 = 210 × 3 = 240 × 3 = 270 × 3 = |
The fast, FUN, and easy way to learn multiplication. Learn the upper times tales in two sittings using mnemonic stories.
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Copyright 2003-2013 Maria Miller
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