Do NowFind the LCM for each set of numbers.

1. 8 and 12

2. 12 and 18

3. 10 and 12

4. 12 and 24

24

36

60

Course 2

3-8 Adding and Subtracting Fractions

24Hwk: p 31

EQ: How do I add and subtract fractions?

Course 2

3-8 Adding and Subtracting Fractions

M7N1.c Add, subtract, multiply, and divide positive and negative rational numbers; M7N1.d Solve problems using rational numbers

From January 1 to March 14 of any given year, Earth completes approximately of its orbit around the Sun,while Venus completesapproximately its orbit.

15

13

The illustration shows what the positions of the planets would be on March 14 if they started at the same place on January 1 and their orbits were circular. To find out how much more of its orbit Venus completes than Earth, you need to subtract fractions.

Course 2

3-8 Adding and Subtracting Fractions

Add. Write the answer in simplest form.

58

+ 18

58

+ 18

= 5 + 18

Add the numerators and keepthe denominator.

= 68

= 34 Simplify.

Course 2

3-8 Adding and Subtracting Fractions

Subtract. Write the answer in simplest form.

911 – 4

11

911

–4

11= 9 – 4

11Subtract the numerators andkeep the denominator.

The answer is in the simplestform.

= 5 11

Course 2

3-8 Adding and Subtracting Fractions

Add. Write the answer in simplest form.

Check It Out: Example 1A

56

+ 16

56

+ 16

= 5 + 16

Add the numerators and keepthe denominator.

= 66

= 1 Simplify.

Course 2

3-8 Adding and Subtracting Fractions

Subtract. Write the answer in simplest form.

710 – 4

10

710

–4

10= 7 – 4

10Subtract the numerators andkeep the denominator.

The answer is in the simplestform.

= 3 10

Course 2

3-8 Adding and Subtracting Fractions

To add or subtract fractions with different denominators, you must rewrite the fractions with a common denominator.

The LCM of two denominators is the lowest common denominator (LCD) of the fractions.

Helpful Hint

Two Ways to Find a Common Denominator

• Find the LCM (least common multiple)

of the denominators.• Multiply the denominators.

Course 2

3-8 Adding and Subtracting Fractions

Add. Write the answer in simplest form.

56

+ 78

56

+ 78

= 5 · 46 · 4

7 · 38 · 3

= 20242124

= 4124

=1 1724

Course 2

3-8 Adding and Subtracting Fractions

= =

Subtract. Write the answer in simplest form.

23

– 34

23

– 34

= 2 · 43 · 4

3 · 34 · 3

Subtract.= – 112

Course 2

3-8 Adding and Subtracting Fractions

=

=

=

8

12

9

12

Add. Write the answer in simplest form.

– 27

+ 13

= Add.

27

+13

=– 2 · 37 · 3

+ 1 · 73 · 7

–

= +– 721

621

121

Course 2

3-8 Adding and Subtracting Fractions

Add. Write the answer in simplest form.

25

+ 56

= 1230

+ 2530

= 3730

=1 730

Divide.

Course 2

3-8 Adding and Subtracting Fractions

Subtract. Write the answer in simplest form.

25

– 12

Subtract.

= 410

– 510

= 110–

Course 2

3-8 Adding and Subtracting Fractions

Add. Write the answer in simplest form.

– 35

+ 12

= Add.

= +– 510

6101

10–

Course 2

3-8 Adding and Subtracting Fractions

Subtract.

12

– = 112

= 612

– 112

= 512

In one Earth year, Jupiter completes about of its orbit around the Sun, while Mars completes about of its orbit. How much more of its orbit

does Mars complete than Jupiter?

12

112

Mars completes more of its orbit than Jupiter does. 512

Course 2

3-8 Adding and Subtracting Fractions

Subtract.

12

– = 512

= 612

– 512

= 112

It takes Michelle hour to drive to work. It takes

Luke hour to drive to work. How much longer

does it take Luke to drive to work?

12

512

It takes Luke hour longer to drive to work.112

Course 2

3-8 Adding and Subtracting Fractions

You TryAdd or subtract. Write each answer in simplest form.

Insert Lesson Title Here

112

13

2. 38

+ 58

1. 57

– 37

3. 4.12

– 14

5. You need a nail to go through a -inch door

and extend an extra inch. How long should the nail be?

114

778

1

in.118

27

+512

1112

Course 2

3-8 Adding and Subtracting Fractions