What are the rules for adding, subtracting, multiplying and dividing fractions? What is the rules for?

Question

adding, subtracting, multiplying and dividing decimals. Can anyone help me with these two questions. Thanks.

Answer 1

Multiplying fractions is pretty simple. All you have to do is multiple across and then reduce. So if you have 3/5 X 4/9, you would multiple 3 times 4 to get the numerator (the top number) and multiple 5 times 9 to get the denominator (the bottom number). So your answer would be 12/45. That can be reduced to 4/15 by dividing both the top and the bottom numbers by 3.



Adding and subtracting fractions is a little more complicated, but still pretty simple. The long way that teachers usually teach you in school is to find a common denominator (the lowest number that the denominators of both fractions will fit into), multiple one or both fractions by a number that will make them both have the common denominator, and then to add/subtract the numerators. For instance, if the problem is 2/3 + 3/4, first you would find the lowest common denominator. In this case, it's 12, since it is the lowest number that both 3 and 4 will go into. Next, you would multiple 2/3 by 4/4 to get 8/12. Then muliple 3/4 by 3/3 to get 9/12. Now that you have two fractions with the same denominator (8/12 and 9/12), you are allowed to add their numerators. This give you 8 +9 = 17 over 12, or 17/12. To subtract two fractions, you would follow the same basic rules, except at the end you would subtract instead of add.



I would teach you the short cut for adding/subtracting fractions (it involves cross-multiplying), but it would probably just confuse you.... You should get this method down pat first.



To divide a fraction by another fraction, all you have to do is flip the second fraction over to get its recipricol and then treat the problem like a multiplication problem. So if you had 6/7 divided by 3/8, you would flip 3/8 over to get 8/3 and then muliple that by 6/7. This gives you 6/7 X 8/3 = 48/21. That can be reduced to 16/7.



Adding and subtracting decimals is like adding and subtracting whole numbers. Simply line the two numbers up so that the decimals are in line with each other, and then add/subtract. Ex:

144.54

+ 10.23

=154.77



I would go into dividing decimals, but it's hard to explain in words. Basically it works the same way as dividing whole numbers except sometimes you must move the decimal of one of the numbers so that both numbers have the decimal in the same place. Google it and you should be able to find a site that shows you how.



Hope this helps :)

Answer 2

To add two fractions: As an example, let's use 1/7 + 3/5 (1) Give them a common denominator. ?/35 + ?/35 (2) Determine what the new value on top would be. Since the denominator of the first needed a 5 to complete it, you have to multiply the top by 5 as well. Similarly for the second number, it needed a 7 to complete it, so you have to multiply the top by 7. (1*5)/35 + (3*7)/35 5/35 + 21/35 (3) Now, just add the numerators. (5+21)/35 = 26/35 The same holds true for subtracting. To multiply two fractions: Let's use 1/7 x 3/5 Note: Multiplication is EXTREMELY simple, compared to addition and subtraction. All you have to do is multiply the numerators and multiply the denominators. (1*3)/(7*5) = 7/15. That's it!! Divide fractions: As an example, let's use 1/3 divided by 7/5. To solve this, all you have to do is flip the second fraction, and then multiply. This flipping is called taking the reciprocal. Therefore 1/3 divided by 7/5 is the same as 1/3 times 5/7 And then you just use your simple rule of multiplying fractions and you get the following: (1*5)/(3*7) = 3/35

Answer 3

ADDING fractions- You need to change the denominator (bottom number) of both fractions so they are the same. Do this by finding the lowest common denominator (LCM). For example 1/2 and 1/3. The LCM is 6. 2 goes into 6, 3 times, so you would multiply the top number by 3 also. Do the same for 1/3. You would then get 3/6 and 2/6.



SUBTRACTING fractions- this is similar to adding. Find a LCM, change the tops of both fractions so the denominator is the same and then subtract like you normally would.



MULTIPLYING fractions- Multiply the top, then the bottom. You do not have to change anything.



DIVISION- Don't change the denominators. If you have 2/3 divided by 2 (2/1) then the rule is to flip the second fraction and change it to multiplication. 2/3 x 1/2



Hope that helps

Answer 4

Since there are no real rules for decimals i assume you meant fractions?



Adding and Subtracting: you can only go straight across and the denominator mus be the same

for ex: 1/2 + 1/2 = 2/2 (NOT 1/3 + 1/4 = 2/12)



Multiplying: You simply multiply straight across as well regardless of denominator.



As for what are the rules are for i do not know, i just follow them.

Answer 5

Rules For Adding Fractions