Lowest common Denominator

It is the smallest common fraction of the Denominator.
We use LCD because it makes fraction operations easier.

Numerator/Amount of pieces
Denominator/Size of pieces
2/3 = 4/6 + 5/6 9/6 1 3/6 or 1 1/2


Multipling


4 x 1/2 2 4/2 = 2 With fractions any whole # over one still equals the original amount.

3/4 x 1/2 = 3/8 when multiplying fractions you do not need a common denominator.

4 3/5 x 2/6 = 23/5 x 2/6 = 46/301 = 16/30 = 1 8/15

2 1/8 x 3 3/5 = 17/8 x 18/5 300/40 divid by 8 both numerator and denominator.

3/4 x 1/3 = 3/12 1/4

7/8 x 6/21
42/168
21/84 = 1/4

Word Problem
A recipe for 4 dozen cookies calls for a 3/4 cup of sugar. How much sugar is needed to make 2 dozen
cookies. 3/4 x 1/2 = 3/8


Adding


Find the LCD first, than add the Numerators together and put the answer to the Denominators.
Example 2/5 = 4/10 9/10 = 9/10
4/10 + 9/10 = 1 3/10

2/3 x by 4 top and bottem = 8/12 + 1/4 x by 3 top and bottem 3/12 + 8/12 11/12

2/3 = 4/6
1/2 = 3/6
7/6 = 1 1/6
1/3 = 2/6


Subtracting

If it's a mix number make it to a improper fraction first, then find LCD.

Word Problem
Tom Anderson set a record when he caught a salmon that weighed 97 1/4 ib. Robert wilson caught a salmon that weighed 74 9/16. How less than the record was this?

97 1/4 - 74 9/16 = 22 11/16