FRACTIONS

Adding fractions

2  +    =  5
7      7       7    When fractions have the same denominators just add the numerators
and bring over the common denominators.

Sometime we need to add fractions that have different denominators.
For example    1   +   1     This requires that we find a common denominator. Why do we
2        3     need to do this. To use an analogy assume that you are going to
add  \$3  +  200 pennies. You would change the \$3 to 300 pennies
and  add 300 pennies + 200 pennies = 500 pennies or you would
change the 200 pennies to \$2 and add \$3 + \$2 = \$5. Either way
you could only get an accurate answer when both quantities
are converted to the same measurement. The same is true with
fractions.

The first step is to find a number that can be divided evenly by 2 and 3. This number is called
a common denominator. If it is the smallest number that can be divided evenly by 2 and 3 we
will call that number the least common denominator (LCD).  The LCD for 2 and 3 is 6.
12, 18, 24 and many others are common denominators but not the LCD. So lets use 6.

1   =                 What we do is divide the new denominator
2        6             by the old denominator and multiply the
answer by the old numerator. This answer is
+ 1  =                   the new numerator. If you follow this procedure
3        6              your work will look similar to this  1  =   3
------------                                                                      2       6

1  =   2
+  3       6
-----------
5
6
Try adding 1/2  +  1/3  using 12 as the common denominator.
Do you get the same answer?    answer

Try these examples:
1)   1/4  +  1/3  =
2)   2/3  +  1/2  =      answer

return to table of content  click