Adding & Subtracting Fractions (Unlike Denominators)

Denominators

• tell how many pieces are in the whole set

• tell how many pieces out of the whole thing we are talking about

• tell how many whole sets there are

Tags

CCSS.3.NF.A.1

CCSS.3.NF.A.2B

Numerators

• tell how many are in the whole set

• tell how many from the whole set we are talking about

• tell how many whole sets there are

Tags

CCSS.3.NF.A.1

CCSS.3.NF.A.2B

7/10 + 3/8

What should be the Lowest Common Multiple/Denominator?

• 20

• 40

• 80

• 8

Answer explanation

40 is the smallest number you'll get when you skip count by 8 and also by 10.

Tags

CCSS.7.NS.A.1C

7/10 + 3/8

What will your new fractions be, with your new common denominator?

• 4/40 + 5/40

• 28/40 + 12/40

• 28/40 + 15/40

• 7/40 + 3/40

Answer explanation

Since you multiplied 10x4, you also need to do 7x4 (=28).

Since you multiplied 8x5, you also need to do 3x5 (=15).

Tags

CCSS.5.NF.A.1

CCSS.5.NF.A.2

What is the total for 7/10 + 3/8, with the new fractions we used?

• 10/40

• 43/80

• 43/40

• 10/18

Answer explanation

Add the numerators. Keep the denominators.

Tags

CCSS.5.NF.A.1

CCSS.5.NF.A.2

Let's subtract now.

3/4 - 2/6

What would be the Lowest Common Multiple/Denominator?

• 24

• 12

• 6

• 4

Answer explanation

12 is the smallest number you say when you skip count by both 6 and 4.

Tags

CCSS.7.NS.A.1C

What would your 2 new fractions be, with your common denominator?

• 9/12 - 4/12

• 3/12 - 2/12

• 9/12 - 6/12

Answer explanation

Since you multiplied 4x3, you need to multiply 3x3 for the numerator (9).

Since you multiplied 6x2, you have to multiply 2x2 for the numerator (4).

Tags

CCSS.4.NF.B.3C

CCSS.4.NF.B.3D

What will you get when you subtract these 9/12 - 4/12?

• 5/24

• 13/12

• 5/0

• 5/12

Answer explanation

Subtract the numerators. Keep the denominators.

Tags

CCSS.4.NF.B.3C

CCSS.4.NF.B.3D