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# Math lessons for the week of Jan 3-6 2012 - PowerPoint PPT Presentation

Math lessons for the week of Jan 3-6 2012. Mrs. Di Todd 5 th grade. Tuesday 1-3-12. Group activity: Show the common factors of 70 and 40: 70 40 Independent activity: Create a Venn diagram of 70 and 40 to display common factors.

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### Math lessons for the week of Jan 3-6 2012

Mrs. Di Todd

Show the common factors of 70 and 40:

70 40

Independent activity:

Create a Venn diagram of 70 and 40 to display common factors.

Number Riddle:

Clue 1: I am a common factor of 28 and 40.

Create factor trees for both numbers.

Clue 2: I am an even number.

Remove all odd numbers

Clue 3: I am not prime.

Remove all prime numbers

What is the number?

Solve each of the riddles below. For each one:

• Make a factor tree and list the factor pairs for each number.

• Find the factors shared by each number (their common factors).

• Use the other clues to find the answer to the riddle.

1. I am a common factor of 27 and 45.

I am an odd number.

When you multiply me by 3, you get a number

greater than 10.

What number am I?

2. I am a common factor of 36 and 48.

I am also a factor of 30.

I am an even number.

I am divisible by 3.

What number am I?

3. I am a common factor of 60 and 100.

I am an even number greater than 4.

I am divisible by 4.

What number am I?

Write your own factor riddle for a classmate that includes

• at least 3 clues. Be sure not to give the answer away before the third clue.

• Exchange papers with a classmate and see if you can solve each other’s riddles.

Hint: Start with the prime numbers and then multiply different combinations of

them to get starting numbers.

Finding Simplest Forms

Find the simplest form for 5/15 and 6/18.

Use your knowledge of prime and composite numbers.

There are 3 ways to find simplest forms:

1. Divide by common factors.

2. Find the GCF and divide by GCF.

3. Use a calculator. See text book page 316.

Math Idea: You can divide by using common factors until 1 is the only common factor, or you can divide by the GCF one time to write a fraction in simplest form.

GCF- greatest common factor

Tell whether the fraction is in simplest form:

• 2/6 2. 1/10 3. 8/20 4. 25/32

Name the GCF of the numerator and the denominator.

• 18/30 6. 8/24 7. 12/15 8. 50/100

Write each fraction in simplest form.

9. 4/10 10. 12/36 11. 24/32 12. 8/20

Independent:

Explain how you would find the simplest form of

16/24 by using both the common factor method and the GCF method.