Adding and Subtracting Positive and Negative Fractions with Unlike Denominators

REMEMBER: YOU MUST HAVE A COMMON DENOMINATOR WHEN ADDING AND SUBTRACTING DENOMINATORS!!!

• FIND THE LEAST COMMON DENOMINATOR.

• ADD OR SUBTRACT THE NUMERATORS AS NORMAL.

• MAKE SURE THAT YOU SIMPLIFY YOUR ANSWERS.

Is this a correct answer?

• Yes, the student correctly added.

• No, you cannot add unlike denominators

• No, 5 + 7 is not 12

• No, 2 + 3 is not 5

• - 1  7/40
• 15/40
• - 1 10/40
• 17/40

-3/8 + 1/4

• 4/32

• -1/8

• 1/8

• -4/32

Re-written with common denominators is:

4/5 - 1/6

• 19/30

• 11/30

• 2/3

• 3/4

Add these fractions. 1/2 + 1/3 =

• 5/6

• 2/5

• 1/5

• 1

When adding and subtracting fractions that have unlike denominators you should . . .

• make mixed numbers

• find a common denominator

• add the denominators and numerators

Ava is going to combine two bags of soil. One bag weighs 7 4/9 pounds and the other weighs 3 1/6 pounds.  Once combined, what will be the total weight of the soil?

• 10 1/3 pounds

• 10 11/18 pounds

• 10  pounds