epdf.pub_cbest-cliffs-test-prep13a9b242c7cb4125e6cca92d00a73d5a41681

Part IV: Mathematics Review
Adding Fractions
To add fractions, you must first change all denominators to their lowest common
denominator (LCD) — the lowest number that can be divided evenly by all the
denominators in the problem. When you make all the denominators the same, you
can add fractions by simply adding the numerators (the denominator remains the
same). For example:
3 =
8
3
8
1 4 + = 2 8
change one-half
to four-eights
1 3 =
4 12
1 4 + = 3 12
change both
fractions to
LCD of 12
7
8
7
12
In the first example, change the 1 ⁄2 to 4 ⁄8, because 8 is the lowest common
denominator, and then add the numerators 3 and 4 to get 7 ⁄8 .
In the second example, you have to change both fractions to get the lowest common
denominator of 12, and then add the numerators to get 7 ⁄12. Of course, if the
denominators are already the same, just add the numerators. For example:
6
⁄11 + 3 ⁄11 = 9 ⁄11
Adding Mixed Numbers
To add mixed numbers, the same rule (find the LCD) applies, but make sure that
you always add the whole numbers to get your final answer. For example:
2 1 ⁄2 = 2 2 ⁄4
+ 3 1 ⁄4 = 3 1 ⁄4
5 3 ⁄4
change one-half
to two-fourths
remember to add
the whole numbers
Subtracting Fractions
To subtract fractions, the same rule (find the LCD) applies, except that you subtract
the numerators. For example:
7
⁄8 = 7 ⁄8
3
⁄4 = 9 ⁄12
− 1 ⁄4 = 2 ⁄8 − 1 ⁄3 = 4 ⁄12
5
⁄8
5
⁄12
200