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sat math
07-06-2013, 01:22 PM
Adding and Subtracting Fractions

To add or subtract fractions, here are some steps:

Find the lowest common denominator (LCD) or any common denominator of the fractions.
Convert the fractions to equivalent fractions having the LCD or the common denominator.
Add or subtract the numerators, keeping the denominator the same.



The LCD of 3 and 5 is 15.

Change the fractions so that each has 15 as the denominator. Remember, you have to multiply the numerator and the denominator by the same number, so that you don’t change the value of the fraction.


and finally add the numerators, but keep the denominator the same


Multiplying and Dividing Fractions

The method is to multiply all the numerators of the fractions together to give the numerator of the answer and
similarly multiply all the denominators together to find the denominator of the answer.


\frac{4}{3} \frac{7}{5}=\frac{4\cdot 7}{3\cdot 5}=\frac{28}{15}

Dividing fractions involves changing the division into a multiplication and then
proceeding as when multiplying fractions. This is achieved by turning the second
fraction upside down and then multiplying instead of dividing.


\frac{4}{3} \div \frac{7}{5}=\frac{4}{3} \frac{5}{7}=\frac{4\cdot 5}{3\cdot 7}=\frac{20}{21}