Download Lesson 5.3: Using Symbols to Add Fractions

February 27, 2015
Lesson 5.3: Using Symbols to Add Fractions
Objective: Use common denominators to add fractions.
- In Lesson 5.1 & 5.2 you used models to add fractions. You
may not always have suitable models to add fractions.
- Lets find a strategy you can use to add fractions without
using a model.
1, 2, 3, 4, 5, 6, 7, 8,
How can you write these numbers in the boxes so the fractions are in order from
least to greatest? (You can only use each number once)
- Try placing the numbers and give it a try
What strategy did you use?
How do you know your placement is correct?
February 27, 2015
Explore: p. 186
Use the following diagrams:
+
=
Case 1: Greatest Sum
+
=
Case 2: Least Sum
- Use the digits 1, 2, 4, and 8 to make the greatest sum and the least sum.
- In each case, use each digit once.
How are you trying to find the greatest sum?
What method are you using to find the
greatest sum?
How do you add 8/1 + 4/2 ?
February 27, 2015
How did you find a lesser sum?
How do you add 1/8 + 2/4 ?
Is 1/8 + 2/4 the least sum?
Equivalent Fractions
We can use equivalent fractions to add
1 + 1
4
3
Use equivalent fractions that have like denominators.
Multiples of 3: ___________________
Multiples of 4: ___________________
_____ is a multiple of 3 and 4.
_____ is a common denominator.
February 27, 2015
Look at the pattern in the equivalent fractions below.
1
4
=
3
12
1
3
=
4
12
So, to get an equivalent fraction, multiply the ______________ and
______________ by the _________ ___________
We may also get equivalent fractions by dividing.
For example, 8 can be written:
10
February 27, 2015
Example:
1) Add: 4 + 5
9
6
Estimate to check the sum is reasonable:
Estimate:
- Use equivalent fractions to write the fractions with a common denominator.
Multiples of __: _________________________________
Multiples of __: _________________________________
When we are finding equivalent fractions, why do we multiply both the
numerator and the denominator?
What other numbers could we multiply by to get equivalent fractions?
What is the advantage of multiplying by 2 instead of 4?
February 27, 2015
Writing an improper fraction as a mixed number:
We write the mixed number as a sum of two fractions, one of which is an
expression for a whole number.
Why do you think 23 was written as 1 5
18
8
More practice
Add:
2) 1 + 4
2
7
3) 1 + 2
4
3
Multiples of __: ______________________
Multiples of __: ______________________
Multiples of __: ______________________
Multiples of __: ______________________
February 27, 2015
Showing this using fraction strips/ circles:
Homework: p. 188 # 1, 2, 4, 5, 6 & 7 (AFQ)