Common Denominators and How to Find Them

First of all, before you can teach subtracting, adding, multiplying, or dividing fractions, you must first explain the significance of common denominators.  Common denominator means when the denominator in two or more fractions are the same.  To find the common denominator, one can use the least common denominator  method or multiply the denominators (bottom numbers) together.  The easiest way to find the common denominator is to list the multiples of the denominators until you get the first number that they both have in common.  When adding or subtracting fractions, a common denominator is needed.  First, make sure that the botton numbers (denominators) are the same. Second, add the top numbers (numerators), putting the answer over the same denominators. Third, simplify the fractions if needed.  When multiplying or dividing fractions, no common denominator is needed.  When multiplying fractions, multiply the numerators of the fractions and write the product as the numerator of the new fraction, and the same thing goes for multiplying the denominators.  Write the answer in lowest terms.  When dividing fractions, change the division to multiplication by flipping the second set of numbers.  Say we have 1over 2 divided by 1 over 4,  we will flip the 1 over 4 to 4 over 1 and follow the rules of muliplying fractions.