Addition of Fractions with Unlike Denominators

Draw

Warm Up:

• 1/4+2/4=

• 3/5+1/5=

Adding Fractions with Unlike Denominators

• Objective: Students will be able to add fractions with unlike denominators

• Today’s goal: Find a common denominator, rewrite, add, and simplify

Key Vocabulary + Big Idea

Denominator: bottom number; tells the size of the parts

Numerator: top number; tells how many parts you have

Equivalent fractions: different fractions that name the same value

Common denominator: a shared denominator so fractions describe same-size pieces
Big idea: To add fractions, they must refer to the same-size parts (same denominator).

Why We Need a Common Denominator

Add Fractions with Unlike Denominators (4 Steps)

1. Find a common denominator (often the LCM; product works but may be bigger)

2. Rewrite each fraction as an equivalent fraction with that denominator

3. Add numerators and keep the denominator

4. Simplify (reduce) and check reasonableness

Teacher Model (I Do):

Steps:​
1. Find a common denominator (often the LCM; product works but may be bigger)
2. Rewrite each fraction as an equivalent fraction with that denominator
3. Add numerators and keep the denominator
4. Simplify (reduce) and check reasonableness

Guided Practice (We Do):

Steps:​
1. Find a common denominator (often the LCM; product works but may be bigger)
2. Rewrite each fraction as an equivalent fraction with that denominator
3. Add numerators and keep the denominator
4. Simplify (reduce) and check reasonableness

Multiple Choice

Why is it important to find a common denominator when adding fractions with unlike denominators?

• It helps to compare fractions easily.

• It allows us to add fractions correctly by making the parts the same size.

• It makes fractions look more complicated.

• It is only needed for subtraction.

Multiple Choice

$$\frac{1}{6}+\frac{3}{4}$$

• 12

• $$\frac{12}{24}$$

• $$\frac{11}{12}$$

•  $$\frac{4}{12}$$

Multiple Choice

• 4/15
• 20/75
• 18/30
• 19/30

Multiple Choice

• 22/20
• 11/10
• 1 1/10
• 1 10/11

Multiple Choice

You drank $$\frac{2}{5}$$ of a bottle of water in the morning and $$\frac{1}{4}$$ ​ in the afternoon. How much did you drink in all?

Hint: $$\frac{2}{5}+\frac{1}{4}=$$

• $$\frac{13}{20}$$

• $$\frac{5}{20}$$

• $$\frac{3}{9}$$

• $$\frac{1}{3}$$