chapter
9
Name
Math Words
prime number a whole number
The numbers 2, 3, 5, 7, and 11 are
greater than 1 that is divisible only by some prime numbers.
itself and the number 1
composite number a whole number The numbers 4, 6, 8, 15, and 21
greater than 1 that is divisible by
are some composite numbers.
more numbers than itself and 1
prime factorization a number
written as the product of prime
numbers
The prime factorization of 50 is
2 3 5 3 5.
greatest common factor (GCF)
the greatest whole number that is a
common factor of two or more
numbers
The greatest common factor of
4, 6, and 12 is 2.
simplest form A fraction is in
simplest form when 1 is the only
common factor of the numerator
and denominator.
2
8
}} is the simplest form of }}.
3
12
Tell if each number is prime or composite. Write a prime factorization for
each composite number. Use exponents if you can.
1. 75
3. 33
Think → The number has factors other
than 1 and itself so it is composite.
75 5 1 3 3 3 5 3 5
4. 56
5. 81
© Macmillan/McGraw-Hill
2. 15
75 = 3 _ 5 _ 5
Answers: 1. given; 2. composite 15 5 3 3 5; 3. prime; 4. composite 56 5 23 3 7; 5. composite 81 5 34
Math at Home Family Guide
Grade 5, Chapter 9 25
Find the greatest common factor (GCF).
6. 25 and 30
7. 18 and 32
8. 81 and 90
Write each fraction in simplest form.
28
56
9. }} 5
1
}}
2
Think → Find the greatest common factor.
28: 1, 2, 4, 7, 14, and 28
56: 1, 2, 4, 7, 8, 14, 28, and 56
GCF is 28.
Divide the numerator and denominator by the GCF.
28 4 28
1
}
} 5 }}
56 4 28
2
16
56
10. }} 5
25
60
18
36
11. }} 5
27
45
12. }} 5
13. }} 5
Problem Solving
Solve.
15. If you sleep about 8 hours each
night, what fraction of each day
are you awake?
14. If you are in school from 9 A.M. to
3 P.M., what fraction of the day are
you in school?
Materials: grocery store flyers and receipts, product coupons, paper, pencil
You can use coupons to save money on groceries, but what fraction of the actual
price are you saving?
• Collect coupons for grocery products. On a sheet of paper, list these products and
their original price. Find the price in flyers, on recent receipts, or at the store.
Estimate any prices you can’t find easily.
• Write the amount of coupon savings over the original price to show what fraction
of the price you would save for each product.
• Reduce the fraction to its simplest form.
• Express all prices in cents and round to multiples of 10 cents to make this easier.
For example, with a 50¢ coupon for orange juice that costs $2.49, you could say
50
1
your savings are about }}, or }} of the price.
5
2
7
5
12
1
2
3
5
6
24
1
4
16
24
250
2
3
Answers: 6. 5; 7. 2; 8. 9; 9. given; 10. }}; 11. }}; 12. }}; 13. }}; 14. }} 5 }}; 15. }} 5 }}
26 Grade 5, Chapter 9
Math at Home Family Guide
© Macmillan/McGraw-Hill
ACTIVITY Fractional Savings