Multiplying Fractions 5th Grade Mrs. Mitchell

Vocabulary Week 3 Reciprocal – the fraction you get once you turn the fraction upside down, meaning the numerator becomes the denominator and the denominator becomes the numerator. Ex: 2/3 is the reciprocal of 3/2. Product – the answer to a multiplication problem. Improper Fraction – fraction where the numerator is larger than the denominator

Math Drill – 5 Minute Frenzy http://www.online-stopwatch.com/

Standard: MCC5.NF.7 Apply and extend previous understandings of division to divide unit fractions by whole numbers and whole numbers by unit fractions. Objective: Students will learn about reciprocals and their importance in dividing fractions. Students will be able to convert a whole number and mixed number to a fraction to solve an equation where a fraction is divided by a whole number or a mixed number.

Reciprocals & Canceling Multiplying and Dividing Fractions

What is a reciprocal? The fraction you get once you turn the fraction upside down. http://www.mathsisfun.com/reciprocal-fraction.html

What pattern do you see here? 2/3 x 4/5 = 8/15 1/2 x 4/7 = 4/14 5/6 x 1/12 = 5/72 What pattern do you see here? 4/8 x 1/2 = 4/16 = 1/4 1/2 x 4/7 = 4/14 = 2/7 1/5 x 3/9 = 3/45 = 1/15

Reciprocal of a Fraction To get the reciprocal of a fraction, just turn it upside down.  In other words swap over the Numerator and Denominator. Examples: Fraction Reciprocal 3/8 5/6 1/3 19/7

Reciprocal of a Mixed Fraction To find the reciprocal of a Mixed Fraction, we must first convert it to an Improper Fraction, then turn it upside down. Example: What is the reciprocal of 2 1/3 ? Convert it to an improper fraction: 2 1/3 =  2. Turn it upside down:  The Answer is: 

So what rule can we write? What pattern do you see? 2/3 x 3/2 = 6/6 = 1 1/2 x 2/1 = 2/2 = 1 5/6 x 6/5 = 30/30 = 1 So what rule can we write?

Let’s Practice http://www.mathsisfun.com/reciprocal-fraction.html

Canceling to Solve Fraction Multiplication Problems

Rules for Multiplying Fractions There are 3 simple steps to multiply fractions: 1. Multiply the top numbers (the numerators). 2. Multiply the bottom numbers (the denominators). 3. Simplify the fraction if needed. Let’s add “canceling whenever possible’, where could we add this step in the list above?

Let’s Practice… http://www.mathplayground.com/fractions_mult.html

Rules for Multiplying Fractions by Whole Numbers There are 4 simple steps to multiply fractions by whole numbers: 1. First turn the whole number to a fraction by placing the whole number over 1. ex: 3 is 3/1 2. Multiply the top numbers (the numerators). 3. Multiply the bottom numbers (the denominators). 4. Simplify the fraction if needed.

Let’s Practice: Individual Practice: http://www.mathopolis.com/questions/q.php?id=1407&site=1&ref=/fractions_multiplication.html&qs=1407_437_430_1408_1409_1410_3569_3570_3571_3572 Individual Practice: http://www.mathsisfun.com/worksheets/print.php?w=38778&ID=32590&Ans=n

Homework for Agenda: Math Worksheet – Front and Back, Even Numbers only - Using Canceling to Multiply Fractions - Finding Reciprocals

Give me the sum of 2/3 and its reciprocal.