Page 91 - ArithBook5thEd ~ BCC

3.7.1 Exercises

Find the products, using pre-cancellation where possible. Check that the answers are in lowest terms.
Express any improper fractions as mixed numbers.
4 7
1. ·
5 12
32 9 15
2. · ·
45 16 6

5 2
3. 12 · ·
8 3
9 21 4
4. · · 2
22 12 7
2
5. of 24.
3
3 2
6. of of 50.
4 3
2 3
7. 2 · 1 .
3 4

Use multiplication to answer the following questions.
3
1
8. What is the area of a rectangle with length 2 feet and width 2 10 feet?
2
1
9. A 12 -gallon fish tank is only three-fifths full. How many gallons of water must be added to fill it
2
up?
2
10. 2 cups of beans are needed to make 4 bowls of chili. How many cups are needed to make 8 bowls?
3
1bowl? 3 bowls?

3.8 Adding and Subtracting Fractions

If I eat a third of a pizza for lunch, and another third for dinner, then I have eaten two thirds in total.
That is,
1 1 2
+ = .
3 3 3
Similar logic applies whenever we add two (or more) fractions with the same denominator –we simply
add the numerators, while keeping the denominator fixed:

a b a + b
+ = .
c c c

A very similar rule holds for subtraction of fractions with the same denominator:

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