Question

how do you find the LCD when subtracting fractions

Answer 1

i dont, let them find themselves

Answer 2

i can show you if you got an example

Answer 3

7/9 and 1/12 and 5/6

Answer 4

is this adding or subtracting? or it really doesnt matter since it amounts to the same concept

Answer 5

subtracting

Answer 6

equate them to some arbitrary number N, and start clearing the denominators

\[\frac{7}{9} -\frac{1}{12} -\frac{5}{6}=N;\text{ start with 9}\]
\[\frac{7(9)}{9} -\frac{1(9)}{12} -\frac{5(9)}{6}=(9)N;\text{ and simplify}\]
\[7 -\frac{3}{4} -\frac{15}{3}=9N;\text{ do 4 next}\]
\[7(4) -\frac{3(4)}{4} -\frac{15(4)}{3}=9(4)N;\text{ and simplify}\]
\[28 -3 -5(4)=28N;\text{ and finish up a little}\]
\[28 -3 -20=28N;\text{ }\]
\[25 -20=28N;\text{ }\]
\[5=28N;\text{ now divide off that 28 and be done with it}\]
\[\frac{5}{28}=N\]

Answer 7

i coulda simplified 15/3 earlier but i didnt see it and it waited for me :)

Answer 8

iam so confused aha

Answer 9

that and 9(4) = 36 .... but other than that lol, the procedure is good

Answer 10

Another way is think of the denominators and which numbers are their multiples. 9 has 1,3,and 9. 12 has 1,2,3,4,6, and 12, and 6 has 1,2,3,6. Look at the numbers and see which numbers they have in common and use the one with the least value. In this case it would be 3 since its the lowest number all 3 denominators have in common

Answer 11

5/36 is the outcome.


what about it got you confused? its jsut letting the numbers find their own common denom

Answer 12

it either that or try and hunt down a common denominator from a seemingly infinite range of mindlesss possibilities

Answer 13

let the numbers do the work

Answer 14

look over what i did and ask me about anything that doesnt make sense .... other than the typos :)

Answer 15

but in my book the example says that the answer is 7/9 = 28/36 and 1/2 = 18/36 and 5/6 = 30/36

Answer 16

yes, we found that 36 is the LCD

Answer 17

so i dont understand why 1/2 changed to 28/36

Answer 18

i mean 1/12 changed to 28/36

Answer 19

1/2 is a value that has many faces, many names, many now styles; but always has the same value

Answer 20

1/12 even; fractions hold value, not looks

Answer 21

i mean 18/36 sorry

Answer 22

1/12 = 2/24 = 3/36

Answer 23

okay so after i find the LCDwhat do i do next

Answer 24

1/2 = 9/18 = 18/38

Answer 25

you dont have to find it, is what im saying; it finds itself

Answer 26

ahh ok. I understand so you are going to look at the multiples of the denominators you have 9, 12, and 6. Multiples of 9: 9,18,27,36,45. multiples of 12 are 12,24,36,48, and the multiples of 6 are 6,12,18,24,30,36, and 42. Look at all the multiples and the first one they all have in common with be the LCD in this case it will be 36. Let me know if you understand and I'll explain the rest

Answer 27

yes i understand that part

Answer 28

ok so now you have an LCD of 36 so you have to make each fraction have that as your denominator. your first fraction is 7/9 so to change the denominator to 36 you multiply 9*4 and what ever you do on the bottom you do on the top so multiply 7*4 as well and you will get 28/36, do you understand that as well?

Answer 29

omg thank you so much i get it now (: your amazing

Answer 30

my pleasureee, then you just do the same with the the other 2 fractions and just add the numerators and simplify =)

Answer 31

kay kay