Adding and Subtracting Fractions

Adding and Subtracting Fractions

Like denominators and unlike denominators

The Basics

• Numerator: Top of fraction (dividend)

• Denominator: Bottom of fraction (divisor)

Open Ended

Describe where the denominator is in a fraction?

Describir donde el denominador es en una fracción?

Multiple Choice

What is the denominator?

¿Cuál es el denominador? $$\frac{3}{5}$$  

• 3

• 5

Multiple Choice

In which problem is the numerator greater than 5?

¿Cuál es el denominador mas grande que 5?

• $$\frac{3}{5}$$

• 4

• $$\frac{7}{3}$$

• $$\frac{1}{8}$$

Add Fractions with Like Denominators

• If denominators are the same...

• Add the numerators

• Denominator does not change

Multiple Choice

$$\frac{7}{9}+\frac{1}{9}=$$  

• $$\frac{8}{9}$$  

• $$\frac{6}{9}$$  

• $$\frac{8}{18}$$  

• $$\frac{7}{81}$$  

Multiple Choice

$$\frac{9}{15}+\frac{4}{15}$$  

• $$\frac{5}{15}$$  

• $$\frac{1}{5}$$  

• $$\frac{13}{15}$$  

• $$\frac{13}{30}$$  

Subtract Fractions with Like Denominators

• If denominators are the same...

• Subtract the numerators

• Denominator does not change

Multiple Choice

$$\frac{12}{17}-\frac{5}{17}$$  

• $$\frac{17}{17}$$  

• $$\frac{7}{17}$$  

• $$\frac{6}{17}$$  

• 1

• 0

Poll

How do you feel about your understanding of adding or subtracting fractions?

• BAD

• Great!

• Ok

Why you need like denominators

• 1/2 + 1/4 is NOT 2/6 (or 2/4, or 2/2)

• You need to obtain like denominators to add or subtract fractions ^ Es necesario obtener como denominadores para sumar o restar fracciones

Open Ended

$$\frac{2}{7}+\frac{3}{5}=\frac{5}{12}$$  

Describe why the problem is wrong?
Describir por qué el problema es un error?



Finding common denominators (multiples)

• Identify the denominators • Identificar los denominadores

• Write or think of the multiples for each number • Escribe los multiplicars

• Find the Least Common Denominator • Busque el denomindor en común

Multiple Choice

$$\frac{1}{8}-\frac{1}{6}$$  

What is the Least Common Denominator?

• 8

• 6

• 48

• 14

• 24

Multiple Choice

$$\frac{3}{5}+\frac{10}{15}$$  

What is the Least Common Denominator?

• 5

• 15

• 75

• 20

• 30

Unlike Denominators

• Find LCM of denominators * Busque LCM

• Multiply numerator and denominator of each fraction by the multiple

• Write the equivalent fractions * Escribe fracciones equivalentes (1/2=5/10)

• Add or subtract the numerators * Agregar o restar las numeradores

Multiple Choice

• 1/12
• 1
• 2/35
• 23/25

Multiple Choice

What is the sum of these fractions?

• 4/5
• 3/20
• 17/20
• 4/20