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Multiplying whole numbers and fractions
Chapter 7 lesson 1 Multiplying whole numbers and fractions cjm12/28/2012
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4/5 of 20 is the same as 4/5 x 20 or 20 x 4/5
How many are in each group? Using 20 counters, divide them into 5 groups. Circle 4 groups (4/5) 4 How many counters are circled? 16 4/5 x 20=16
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Example (pg 292) 2/3 of 12 or 2/3 x 12 Using 12 counters, divide them into 3 groups. (Hint: the denominator tells you how many groups; the numerator tells you how many to circle.) Circle 2 groups. How many counters are circled? 8 2/3 x 20= 8
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Try this! Draw an array for the problem on page 292.
X X X X ¾ x 16= X X X X How many counters did you circle? X X X X How many groups should you draw? X X X X 4 12 How many groups should you circle? So, 12 of Susan’s stamps are from the United States and 4 stamps are not. 3
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8 rows 2 7 14 14 Share & Show 7/8 x 16= How many rows of counters?
How many are in each row? 7 Circle ____ rows to solve. How many counters are circle? 14
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Use a model to solve. 2/3 x 18= 2/5 x 15= 2/3 x 6=
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Other methods to solve these problems:
15 5. 5/8 x 24= 5 8 Multiplication: X 24 = 5 x 24= 120 8 The 8 slides over. 15 120 is an improper fraction: divide to simplify. 8) 120 -120 15 x 8 = 120 Important!! Multiply the numerator by the whole number.
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Other methods to solve these problems:
24÷8=3 Division, then multiplication: 3 5 8 15 x 24= 8 ÷8=1 1 Both numbers (24 & 8) can be divided by 8. (Reduce by 8) 1. Look at the denominator and the whole number. Is there a number that will go into both of them? 2. Now with 1 on the bottom, it is just 5 x 3= 15.
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