Sunday, May 10, 2009
Adding fractions is really simple. First you have to find the lowest common denominator (the lowest number that both denominators go into, often you can find the lowest common denominator by multiplying both denominators), then multiply the numerators, by how much you've multiplied the denominator. If it is a mixed fraction, you add the whole numbers first, then add the fractions. If the fractions are improper, change it to a mixed number and add the extra whole to the answer.
Subtracting fractions is almost just as simple. Instead of adding, you subtract. You find the lowest common denominator and then you multiply the numerators by the same amount of times you multiplied the denominators, then subtract the numerators, and often, you simplify at the end. If it is a mixed fraction, subtract the whole numbers, and fractions, if possible. If it isn't possible to subtract the fractions, subtract one, from the first mixed number, then add the numerator and denominator, and use the sum of that to replace the first numerator in the fraction; now it is a improper fraction. Finally, subtract normally.
Multiplying fractions is a bit easier. You simply multiply the numerators and denominators, then simplify. To multiply mixed numbers, convert them to improper fractions, then multiply, then convert them back to mixed numbers.
Probably the most confusing of all, is division. There are two ways to divide, using a ratio table, or using the reciprocal. To use the ratio table, we place the fraction that is being divided on the left side of the table, and the divisor fraction on the right side of the table. Here, we focus mostly on the divisor fraction. Using division and multiplication, make that divisor fraction into a whole. What you do to the divisor fraction, you must do to the fraction that is being divided. Your answer will be the results of the fraction being divided.
To use the reciprocal, it is a lot, lot easier. All you do is turn the second fraction upside down, and multiply.