Common Denominators

Finding the Common Denominator

• The Denominator is the number on the Bottom of the Fraction

• Comparing fractions with the same denominator is easy; whichever has the biggest numerator (top number) is the biggest (i.e. 5/9 is bigger than 4/9)

• But when fractions have different denominators we have to find a number that both of them will divided into (a common denominator)

Finding the Common Denominator (continued)

• For example, to compare 2/3 and 3/4 we need to find a number that both 3 & 4 will divide into; they will both divided into 12

• So now we can change the number on the bottom to 12 .... but what do we do to the numbers on the top?

• We must multiply the top number by however many times its bottom number divides into the common denominator

• 2/3 becomes 8/12, and 3/4 becomes 9/12

Multiple Choice

What is the lowest common denominator of 1/4 and 1/3?

• 4

• 3

• 12

• 8

Multiple Choice

What is the lowest common denominator of 1/9 and 2/3?

• 6

• 3

• 9

• 21

Multiple Choice

What is the lowest common denominator of 1/2 and 3/7?

• 2

• 14

• 7

• 28

Multiple Choice

What is the lowest common denominator of 1/4 and 2/5?

• 5

• 25

• 10

• 20

Multiple Choice

Which is the Biggest?

2/3, 3/4, 3/6

• 2/3

• 3/4

• 3/6