Adding And Subtracting Fractions With Unlike Denominators

Essay, Research Paper

Adding and Subtracting Fractions With Unlike Denominators

To add and subtract fractions with unlike denominators, you must first copy down the problem, and make sure it’s setup horizontally. Be sure to include your addition or subtraction signs between your two fractions. After that, you have to find your Lowest Common Denominator (LCD), which you find by looking at a multiplication chart, and following the two numbers that are the denominators, and the first two numbers that are the same is your LCD (if no two are the same, use the chart like a multiplication chart, and use the number in the middle as your LCD). The next step is to write out the abbreviated word LCD about 2 inches below the problem so that you have some space to do work, and put an equals sign next to it. You then write your LCD in the spot which you just made for it, and you have to use your LCD as the denominator in a new problem, with the LCD as both of the denominators for the problem, and put either the addition sign or the subtraction sign between your two half-completed fractions, which you take from your old problem, and use the same one. Be sure to put a fraction line above the denominator in your new problem. To find out your new numerators, you should check your old denominators, and your new denominators. Find out what you have to multiply the old denominators by the new denominators to see what you should multiply the old numerator by to get a new numerator for your new problem. Do the same on your second fraction. Now you have to add or subtract the two fractions. Since the denominators should be the same, when you add or subtract them, they should remain the same. As for the numerators, they should act just like a normal addition or subtraction problem, and the answer goes as the numerator and answer for your problem. Be sure to have your fraction line for the answer!

Make sure that the fraction can be reduced, and if it can be reduced, reduce it! You reduce it by finding your Greatest Common Factor (GCF) and dividing both the numerator and denominator by the GCF. You find the GCF by finding all of the factors, and the two factors that the numerators and denominators have that are the highest number is your GCF. If the greatest common factor is one, than the fraction is already in lowest terms.

If you end up with an improper fraction, read on. If you want to change an improper fraction into a mixed number, you have to divide. Divide the numerator by the denominator, and your whole number in your quotient is still your whole number in your mixed number, the remainder is the numerator of your fraction, while the denominator stays the same in your mixed number. Be sure to put in a fraction line in between your numerator and denominator in your mixed number, and an equals sign before your fraction to show that the fraction is equal to the mixed number that you just made.


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