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Q: Do you always have to have like numerators in fractions before you can add or subtract?

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First find the lowest common denominator and then adjust the fractions accordingly before subtracting the numerators

I learned to always change the denominators before adding or subtracting the numerators. You must always have a common denominator before adding or subtracting.

Because think of like fractions as the same things.. you can subtract halves from halves for example, but what does it mean to take away a half from a third?By converting them into like fractions, we can add or subtract them easily.

because it would be diffcult to understand.[you don't add or subtract the demonters]

The denominators must be the same before you can add or subtract fractions.

Before fractions can be subtracted or added, they must have the same denominators. Therefore, each of the denominator and numerator of a pair of dissimilar fractions should be multiplied by a number chosen so that the resulting fractions will have the same denominators. This is most readily accomplished by multiplying each fraction by the denominator of the other. Once the fractions have a common denominator, their numerators can be subtracted or added to obtain the proper value of the numerator of the sum or difference, which will have the common denominator thus determined. It may, of course, be possible to simplify the resulting fraction.

So that you only have to add/subtract the numerator which makes it much easier.

To multiply two fractions, the numerator (top part) of the result is the product of the numerators, and the denominator (bottom part) of the result is the product of the denominators. There is no need to convert to a common denominator first; this is only necessary to add, subtract, or compare fractions. For example, 1/2 x 5/7 = (1x5) / (2x7) = 5/14. Note that it is easier to do any simplifications BEFORE doing the actual multiplication.

You DO need a common denominator to add, subtract, or compare fractions. You DO NOT need a common denominator to multiply or divide fractions.

Because the answers will be wrong when adding or subtracting them if they don't have a common denominator.

The question is based on a complete misunderstanding of what is required. Unlike denominators are NOT required!

If their denominators are different then find their lowest common denominator by means of their lowest common multiple remembering to adjust their numerators accordingly before adding or subtracting.

Common Denominator means that the denominators in two (or more) fractions are common, or the same. The common denominator is important because before you can add or subtract fractions, the fractions need to have a common denominator.Sometimes fractions have different denominators, like 2/3 and 3/4. If you want to add or subtract them, they need to have the same denominator. In order to do that, you find a common denominator which is the same thing as a common multiple, only with denominators.

The answer is 13/20. The answer is gained by converting both the numerators (upper value of fractions) and denominators (lower value of fractions) into a common value before attempting to add the fractions. Hence 2/5 = 8/20 and 1/4 = 5/20 so the answer therefore is 8/20 + 5/20 = 13/20!

This can be done in different ways, but it is probably easiest to convert all the mixed fractions to improper fractions first. Then multiply all the numerators, and all the denominators. You can do simplifications either before multiplying, or after multiplying.

It is 15/60, which can be simplified, but probably best to see if you need to add or subtract other fractions of an hour before simplifying.

Before you can add or subtract, both fractions must have the same denominator, andmaking that change without changing the value of either fraction is your job. The bestchoice for a 'common' denominator is usually the least common multiple of the originaldenominators.

You multiply the numerators, and the denominators, separately. a/b x c/d = ac/bd.It often helps to do any simplification before you do the actual multiplication.

you change the denomoninator to the biggest number It depends on what you are trying to do. To add or subtract the denominators need to be the same, so you need to change one or both fractions to equivalent fractions with the same denominator before adding or subtracting. To multiply, you just multiply the numerators and the denominators. To divide, take the fraction that you are diving by and flip it over and multiply just like you do for multiplication of two fractions. Add or subtract: 1/2 + 1/3 = 3/6 +2/6 = 5/6 Multiply: 1/2 X 1/3 = 1/6 Divide: 1/2 / 1/3 = 1/2 X 3/1 = 3/2

Multiply the numerators of both fractions. That's the numerator of the result.Also, multiply the denominator of both fractions. That's the denominator of the result. Simplify as appropriate. Actually, it helps to simplify before doing the actual multiplication.

To get the right answer. If you add 1/3 and 1/4, you might not be as successful as when you add 4/12 and 3/12.

Then they have the same units. As a comparison, if you want to add different units of length, for instance meters and centimeters, you have to convert everything to meters (or everything to centimeters), before you add it.

First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.First you find a common multiple of the denominators. The least common denominator is handy but not essential. This number will be the denominator of the answer - before simplification.For both fractions find an equivalent fraction whose denominator is this common denominator.Carry out the subtraction on the new numerators to give the numerator of the answer.Simplify the result for the final, simplified answer.

You multiply the numerators of both fractions, and place the result in the numerator of the result. Similarly, the denominator of the result is the product of the denominators of the individual fractions. For example: 2/3 x 3/7 = (2x3) / (3x7) = 6/21 You can simplify the result in the usual way. However, it is usually simpler to simplify before doing the actual multiplication. In the above example, you can cancel (eliminate) the 3 in the numerator with the 3 in the denominator before doing the actual multiplication.

To Divide Fractions: Invert (i.e. turn over) the denominator fraction and multiply the fractions Multiply the numerators of the fractions Multiply the denominators of the fractions Place the product of the numerators over the product of the denominators Simplify the Fraction Example: Divide 2/9 and 3/12 Invert the denominator fraction and multiply (2/9 ÷ 3/12 = 2/9 * 12/3) Multiply the numerators (2*12=24) Multiply the denominators (9*3=27) Place the product of the numerators over the product of the denominators (24/27) Simplify the Fraction (24/27 = 8/9) The Easy Way. After inverting, it is often simplest to "cancel" before doing the multiplication. Cancelling is dividing one factor of the numerator and one factor of the denominator by the same number. For example: 2/9 ÷ 3/12 = 2/9*12/3 = (2*12)/(9*3) = (2*4)/(3*3) = 8/9 Source: www.aaamath.com