Add fractions by finding the lowest common denominator (LCD); simplify your answers where possible
Home / 7th grade / Number / Fractions / Add fractions using LCD
Fractions with different denominators can be added by changing the fractions so that they share a common denominator.
Given the sum:
1/3 + 1/2
you do this by first finding the Lowest common multiple (LCM) of the denominators of both fractions.
The LCM is the smallest multiple shared by a set of numbers. For instance, some shared multiples of 2 and 3 are 6, 12 and 18, and the LCM is the smallest of those numbers which is 6. The LCM of 2 and 5 is 10 since 10 is the smallest multiple shared by 2 and 5.
Rewrite both fractions to use that LCM by multiplying both the numerator and the denominator by the same number. So, to convert 1/3 to have a denominator of 6, multiply both top and bottom by 2, giving 2/6.
Once you have converted both fractions so that they share the same denominator, you can add the fractions by adding the numerators.
1/3 + 1/2 = 2/6 + 3/6 = 5/6
Below is a table showing the first 6 question answer pairs for the topic "Add fractions using LCD" as used in the lessons for this topic. Our games and tests for the topic use these 6 items plus 10 additional question answer pairs.
The topic "Add fractions using LCD" is in the category Number for 7th grade (ages 12 to 13).
Home / 7th grade / Number / Fractions / Add fractions using LCD
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