Arithmetic Grade Five
Lesson Ninety-nine: Adding Mixed Numbers
Adding mixed numbers with unlike denominators is a little more complicated
than any of the other operations we've seen so far simply because there are
more steps involved.
Sample Problem: 3 1/5 +
2 1/4.
Step One: Find lowest common denominator (LCD). The LCD of 5
and 4 is 20.
Step Two: Convert fractions. Change 1/5 to 4/20 and 1/4 to
5/20.
Step Three: Add whole numbers.
3 4/20 + 2 5/20 =
5 + 4/20 + 5/20.
Step Four: Add the fractions.
5 + 9/20.
Step Five:
Reduce the fraction (if necessary) 5 9/20.
ANSWER: 5 9/20.
Here's another example:
Sample Problem: 1 2/9 +
2 2/7.
Step One: Find LCD. The LCD of 9 and 7 is 63.
Step Two: Convert fractions. Change 2/9 to 14/63 and change
2/7 to 18/63.
Step Three: Add whole numbers.
1 14/63 + 2 18/63 =
3 + 14/63 + 18/63.
Step Four: Add the fractions.
3 + 32/63.
Step Five:
Reduce the fraction (if necessary) 3 32/63.
ANSWER: 3 32/63.
Now you get to try a few for yourself.
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