multiplying, with multiple digits · what we know about multiplication: ... •there are lots of...
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Multiplying, with Multiple DigitsGrade Four Mathematics
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What we know about multiplication:
• Multiplication combines/adds/puts together equal-sized groups.
• There are lots of ways to represent multiplication.
• We have practiced multiplication before.
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What we know about digits/place value:
• The “place” a number is in, when we talk about a multi-digit number tells us how big it is.
3 8 2Left = Larger Place Value
Remember, each time we bump to the left, we’re dealing with a number that is ten times bigger.
100’s 10’s 1’s
When we look at a number in expanded form, it gets even easier to see place value:
382 = 300 + 80 + 2
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Now, let’s put them together!
42 x 3 = _______How could we solve this?
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A simple checklist:
• Expand the bigger number• Multiply• Combine/Make sure your answer is in
standard form
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Let’s practice!
12 x 2 = _______Remember: 1. Expand 2. Multiply3. Standard Form
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Let’s practice!
11 x 5 = _______Remember: 1. Expand 2. Multiply3. Standard Form
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Next Step: REGROUPING
Regrouping is making groups of tens.
In multiplication or addition, it might be called carrying.
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Remember this example?
42 x 3 = _______ How could we solve this?
42 x 3 40+2 = 42
= (40 x 3) + (2 x 3)= 120 + 6= 126
Did we have to do any regrouping?
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What if it looked like this, instead?
24 x 3 = _______How could we solve this?
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Let’s practice!
27 x 3 = _______Remember: 1. Expand 2. Multiply3. Add to get Standard Form
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Let’s practice!
21 x 8 = _______Remember: 1. Expand 2. Multiply3. Add to get Standard Form
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Let’s practice!
19 x 5 = _______Remember: 1. Expand 2. Multiply3. Standard Form
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Word ProblemsSomething you already know, but is worth reviewing
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Saying and Seeing Multiplication
“times”“multiplied by"
In written word problems, you might have to look for other hints: “groups of"“bags of"“rows of"“five in each box"
When we talk about multiplication, you might hear:
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Let’s Practice
• Deborah works at a store that makes shoes for pets. One day, she has 12 customers that each want a set of boots for their dogs. How many shoes will she have to make?
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Let’s Practice
• The next day that Deborah works, a customer brings in eleven tarantulas to have shoes made for them. How many shoes will Deborah have to make?
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Let’s Practice
• Hassan helps his father set the table for a big dinner. His aunty, uncle, three cousins, and four of their neighbours will all be coming. His father says that each guest needs a cup, a plate, a knife, a fork, a spoon, and a napkin. How many items will Hassan have to bring to the table?
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Teeny Challenge
• James knows that there are 40 quarters in a roll. How much money is in a roll of quarters?