Adding Fractions with unlike denominators

Adding Fractions with unlike denominators

Vocabulary

• denominator-bottom number in a fraction

• numerator-top number in a fraction

• multiple-the product of one number multiplied by another number.

• sum-answer to an addition problem

• Least Common Multiple(LCM)-smallest number both numbers will evenly divide into

2 Ways to find a common denominator

• multiply the denominators together

• find the least common multiple

• sometimes the LCM is one of the denominators. check to see if one of the denominators will divide into the other. If it does, that is your least common multiple.

Multiple Select

Choose 2 possible common denominators for these fractions.

5/6 and 3/8.

• 24

• 18

• 48

• 36

• 56

Fill in the Blank

Why is 24 a better choice for a common denominator than 48?

Next, find equivalent fractions

• remember that any fraction where both the numerator and the denominator are the same,(4/4, 6/6, 8/8, etc...) is equal to 1. That is why you get an equivalent fraction when you multiply by 2/2.

• whatever you do to the bottom number, you must also do to the top number.

Multiple Choice

If you are adding the fractions ⅕ + ¾ , the LCM is 20. What are the new, equivalent fractions.

•  $\frac{1}{20}+\frac{3}{20}$  
  

•  $\frac{4}{20}+\frac{15}{20}$  
  

•  $\frac{10}{20}+\frac{15}{20}$  

•  $\frac{4}{20}+\frac{12}{20}$  

Open Ended

Find the common denominator and equivalent fractions for this equation.

 $\frac{4}{5}+\frac{1}{3}$  

Open Ended

Find the common denominator and equivalent fractions for this equation.

 $\frac{2}{7}+\frac{2}{3}$  

Once you have your common denominator and equivalent fractions, then you add the numerators.

• the denominators stay the same when adding

•  $\frac{2}{7}+\frac{2}{3}=\ \ \ \frac{6}{21}+\frac{14}{21}=\frac{20}{21}$  

Open Ended

 $\frac{1}{4}+\frac{2}{3}=$  

Open Ended

 $\frac{3}{4}+\frac{5}{6}=$  

Any Questions so far?

Answer the following practice problems

• answers may not be in simplest form, we'll go over reducing and simplifying tomorrow

• I will work each problem on the board after everyone has answered

• Ask questions if you don't understand something, you will have a quiz on Friday to complete for a grade.

Multiple Choice

 $\frac{4}{5}+\frac{5}{6}=$  

•  $\frac{9}{30}$  

•  $\frac{25}{24}$  

•  $\frac{49}{30}$  

•  $\frac{9}{11}$  

Multiple Select

 $\frac{1}{4}+\frac{5}{6}=$  

•  $\frac{26}{24}$  

•  $\frac{13}{12}$  

•  $\frac{6}{24}$   

•  $\frac{6}{10}$  

Multiple Choice

 $\frac{3}{4}+\frac{2}{5}=$  

•  $\frac{6}{20}$  

•  $\frac{6}{9}$  

•  $\frac{19}{14}$  

•  $\frac{21}{20}$  

Multiple Choice

 $\frac{1}{4}+\frac{3}{8}=$  

•  $\frac{4}{8}$  

•  $\frac{5}{8}$  

•  $\frac{7}{5}$  

•  $\frac{4}{12}$  

Multiple Choice

 $\frac{2}{3}+\frac{1}{9}=$  

•  $\frac{7}{9}$  

•  $\frac{3}{12}$  

•  $\frac{5}{4}$  

•  $\frac{3}{27}$