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Lesson 5 — Activity 2: Working with Fractions with UnLike Denominators
Completion requirements
Lesson 5 — Activity 2: Working with Fractions with Unlike Denominators
Getting Ready
In the last activity, you practised adding and subtracting fractions and mixed numbers with the same denominator.
Now you will look at fractions
where the denominators are not the same. It is necessary to make them
the same before you can add or subtract a fraction.
Let's look at an example:
You have allowed yourself half of your allowance to spend on books.

You can get a common denominator by finding the equivalent fractions with the lowest common denominator (LCD).

Let's say you have a blueberry pie. Your friend Sari eats 1/2 of the pie and you eat 1/8 of the pie. How much is left over?
Start with two circles. Each circle will represent a pie.
Draw a line down the middle of the first circle and colour it. This will represent half a pie.
Divide the second circle into eight equal parts. Colour one part of the circle. This represents 1/8 of the pie.
The
drawings are not common so we cannot add the two fractions yet.
However, you can divide the first picture into eight equal pieces by
drawing three more lines. This now cuts the pie into eighths as well. Now it
is possible to subtract the fractions.
Now you know how much of the pie was eaten. How much is left? Simple! Count the uncoloured portions of the final picture.
There is 3/8 of the pie left.
Try This:Here is a problem for you to solve.A punch recipe calls for 3/4 cups of pop and 2/3 cups of juice.How much punch will there be in total?
1. Find the lowest common multiple of the denominators. This will be the lowest common denominator (LCD).
2.
Multiply each fraction by the number of times the denominator goes into
the LCD. Remember to multiply both the top and the bottom.
3. Make an equation with your new fractions and solve. You will have an improper fraction as your answer!
4: {4, 8, 12, 16}

Your answer for the above problem was an improper fraction.
Before you are done with the problem, you must reduce this improper fraction by dividing the denominator into the numerator.
There will be 1 5/12 cups of punch in total.
Let's now try the punch problem using mixed numbers.
The punch recipe calls for 2 1/4 cups of pop and 2/3 cup of cranberry juice. How much punch will there be in total?
Then do the following: