 ## Presentation on theme: "Adding and Subtracting Fractions"— Presentation transcript:

Course 2 3-8 Adding and Subtracting Fractions Do Now Find 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 24 Hwk: p 31

Course 2 3-8 Adding and Subtracting Fractions EQ: How do I add and subtract fractions? M7N1.c Add, subtract, multiply, and divide positive and negative rational numbers; M7N1.d Solve problems using rational numbers

Course 2 3-8 Adding and Subtracting Fractions From January 1 to March 14 of any given year, Earth completes approximately of its orbit around the Sun, while Venus completes approximately its orbit. 1 5 3 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. 5 8 1 8 + 5 8 1 8 5 + 1 Add the numerators and keep the denominator. + = 8 6 8 3 4 = = Simplify.

Course 2 3-8 Adding and Subtracting Fractions Subtract. Write the answer in simplest form. 9 11 4 11 Subtract the numerators and keep the denominator. 9 11 4 11 9 – 4 = 11 = 5 11 The answer is in the simplest form.

Course 2 3-8 Adding and Subtracting Fractions Check It Out: Example 1A Add. Write the answer in simplest form. 5 6 1 6 + 5 6 1 6 5 + 1 Add the numerators and keep the denominator. + = 6 6 = = 1 Simplify.

Course 2 3-8 Adding and Subtracting Fractions Subtract. Write the answer in simplest form. 7 10 4 10 Subtract the numerators and keep the denominator. 7 10 4 10 7 – 4 = 10 = 3 10 The answer is in the simplest form.

Two Ways to Find a Common Denominator
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. Two Ways to Find a Common Denominator Find the LCM (least common multiple) of the denominators. Multiply the denominators. The LCM of two denominators is the lowest common denominator (LCD) of the fractions. Helpful Hint

Course 2 3-8 Adding and Subtracting Fractions Add. Write the answer in simplest form. 5 6 7 8 + 5 6 5 · 4 6 · 4 20 24 = = 7 · 3 8 · 3 21 24 + 7 8 = = 41 24 17 24 = = 1

Course 2 3-8 Adding and Subtracting Fractions Subtract. Write the answer in simplest form. 2 3 3 4 8 2 3 2 · 4 = = 12 3 · 4 9 3 4 3 · 3 = = 12 4 · 3 = – 1 12 Subtract.

Course 2 3-8 Adding and Subtracting Fractions Add. Write the answer in simplest form. 2 7 1 3 + 2 7 + 1 3 = 2 · 3 7 · 3 + 1 · 7 3 · 7 = + 7 21 6 1 21 = Add.

Course 2 3-8 Adding and Subtracting Fractions Add. Write the answer in simplest form. 2 5 5 6 + 12 30 25 30 = + 37 30 7 30 = = 1 Divide.

Course 2 3-8 Adding and Subtracting Fractions Subtract. Write the answer in simplest form. 2 5 1 2 = 4 10 5 = 1 10 Subtract.

Course 2 3-8 Adding and Subtracting Fractions Add. Write the answer in simplest form. 3 5 1 2 + = + 5 10 6 1 10 = Add.

Course 2 3-8 Adding and Subtracting Fractions 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? 1 2 12 1 2 = 12 = 6 12 1 = 5 12 Subtract. Mars completes more of its orbit than Jupiter does. 5 12