how do i find the LCD?

- anonymous

how do i find the LCD?

- Stacey Warren - Expert brainly.com

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- anonymous

Find multiples of each the denominators and see which ones they all have in common. Then choose the smallest of those to be your LCD.

- anonymous

For example:
Finding the LCD of 2/3, 5/12, and 7/15 we would list multiples of 3, 12 and 15

- anonymous

The other method involves factorizing your denominator

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- anonymous

And is often a bit faster.

- anonymous

so what if i have big number like, 220 and say 100....?

- anonymous

Yeah, that's when factorizing helps.
What are the factors of 220?

- anonymous

how do you find the factors?

- anonymous

22 * 10 = 220
(11*2)*(5*2) = 220
So the factors of 220 are 2*2*5*11

- anonymous

oh, ok thanks!!

- anonymous

Does that make sense as to how you break them down?

- anonymous

yea sort of, i'm a little bit rusty when it comes to math....

- anonymous

So now, what are the factors of 100?

- anonymous

Pick two numbers you can multiply to get 100

- anonymous

hold up one second

- anonymous

ten and one??

- anonymous

ten times one is ten.

- anonymous

ok sorry, i ment ten times ten and 1 times 100

- anonymous

yeah, don't bother with 1, it's not useful when factoring, because you can factor infinitely many ones from any number

- anonymous

But \(10\times 10\) is good. So now, what two numbers do you multiply to get 10?

- anonymous

5x2 and 1x10 are the only ones i can think of right off the top of my head

- anonymous

Right, those are the only ones. But again, the 1x10 is not useful. So we'll use 5x2

- anonymous

So that means that
\(100 = 10\times 10\)
\(100 = (5\times 2)\times (5\times 2)\)

- anonymous

So the factors of 100 are?

- anonymous

10?

- anonymous

No. 2*2*5*5

- anonymous

sorry, like i said, a bit rusty

- anonymous

You take each number in your fully factored form those are your factors

- anonymous

In this case we had 2*5*2*5 = 100, so 2, 2, 5, 5 would be our factors.

- anonymous

oh, wow, thank you so much for your help!!!

- anonymous

Ok, so now we take the factors of 100 and the factors of 220 and compare them:
100= 2*2 * 5*5
220= 2*2 * 5 * 11

- anonymous

and the lowest is two, so the LCD would be 2??

- anonymous

No, that's the LCF

- anonymous

ok so whats the LCD then?

- anonymous

The lowest common factor is 2, but the lowest common divisor is actually bigger than 100, or 220

- anonymous

And we see that if we want them to have the same factors, we need a 11 times 100 and a 5 times 220

- anonymous

What is 11 * 100?

- anonymous

im looking for the lowest common denominator, not the divisor..

- anonymous

100= 2*2 * 5*5
220= 2*2 * 5 * 11
Sorry I meant denominator

- anonymous

oh ok, i was getting a bit confused fro a second,

- anonymous

So again, both of our numbers have 2 2's, and one 5.

- anonymous

But one has an extra 5, and the other has an 11.

- anonymous

Do you see that?

- anonymous

yep i do!

- anonymous

Ok, so we have to make them the same

- anonymous

So we need to multiply 100 times 11, and 220 by 5 and they will have the same factors and therefore be the same number. And that number is our LCD.

- anonymous

oh ok!

- anonymous

So what is 5 * 220, and 100 * 11?

- anonymous

1100

- anonymous

yep.
Now lets have you try it with either another problem you have, or my earlier example

- anonymous

ok lets see, how about, 95 and 100

- anonymous

Ok, so first factor them like we did before, 100 is easy since we already had that one the last time.

- anonymous

yep and its 10x10

- anonymous

No, you can factor that further remember?

- anonymous

10 is 5*2, so 100 is 5*2 * 5*2

- anonymous

oh yea sorry, i am so sorry i apparently have lack of memory

- anonymous

anyways, do go on...

- anonymous

Ok, so factor 95

- anonymous

ok 5x19 is one i know

- anonymous

but i cant think of any others

- anonymous

That's good. There are no others.

- anonymous

oh ok

- anonymous

So list the factors of 100, and the factors of 95 side by side and see which ones they have in common and which ones they do not.

- anonymous

ok so, 100: 5x2 5x2 and for 95: 5x19
so the all have fives

- anonymous

Ok, which ones do they not have in common?

- anonymous

19 and 2

- anonymous

Ok, specifically if we wanted to make them the same, what would we need to multiply by 100

- anonymous

not really sure....

- anonymous

100 has all the ones 95 has except?

- anonymous

19

- anonymous

Good. And 95 has all the ones 100 has except?

- anonymous

2

- anonymous

Close. It's actually two 2's and a 5. You have to count how many each one has.

- anonymous

oh ok so with that how do you make them the same?

- anonymous

Well you multiply the 100 by the ones it's missing (19) and the 95 by the ones it's missing (2*2*5)

- anonymous

And they should be the same.

- anonymous

and it would equal to 1900

- anonymous

100 * 19 = 1900, what about 95*2*2*5?

- anonymous

it equals the same, 1900

- anonymous

Yep, that's your LCD

- anonymous

Ok try another one on your own.

- anonymous

i will! thanks for all your help!!

- anonymous

Any time =)

- anonymous

wow i just did one on my own and i got it right, thank you for helping me understand!

- anonymous

Very welcome! =)

- anonymous

but i might need help on something else, if you have the time

- anonymous

Oh, when you can, go ahead and give me a medal, that's how the site determines whether or not the question is answered.

- anonymous

Of course, just start a new question and I'll take a look.

- anonymous

ok, i have these problems where im supposed to change a percent that is a mixed number into a fraction (in lowest terms) and the book gives me no help on how to do it

- anonymous

Ok, well start by turning the mixed number into a fraction.

- anonymous

for example, 5 3/8 percent into a fraction

- anonymous

Right, so start by turning the 5 3/8% into a improper fractional percentage

- anonymous

Basically ignore the percent for now.

- anonymous

ok hold up

- anonymous

dont you multiplie the 5 by 3 then add 8, or am i getting this mixed up

- anonymous

dont you do this: 5x3+8 then keep eight as your denominater

- anonymous

No, for improper fractions, you need to rewrite 5 as \(\frac{x}{8}\)

- anonymous

Then add it to the 3

- anonymous

sorry, i dont know what that is

- anonymous

5 and 3/8
\[= 5 + \frac{3}{8}\]\[ = \frac{5}{1} + \frac{3}{8}\]
\[= \frac{5}{1} * 1 + \frac{3}{8}\]
\[= \frac{5}{1}*\frac{8}{8} + \frac{3}{8}\]
\[= \frac{40}{8} + \frac{3}{8}\]
\[= \frac{43}{8}\]

- anonymous

ok, i kind of get it but kind of dont, if that makes any sense

- anonymous

like where did the one and the eight come from>

- anonymous

Well, you can always multiply 1 times something and get the same thing right?

- anonymous

right...

- anonymous

\[\frac{5}{1} = \frac{5}{1}*1\]

- anonymous

oh ok....

- anonymous

And any number over itself is 1 right?

- anonymous

right

- anonymous

\[\frac{8}{8} = 1 \implies \frac{5}{1}= \frac{5}{1}*1 = \frac{5}{1}*\frac{8}{8} = \frac{40}{8}\]
This is just a very long way to say that
\[5 = \frac{40}{8}\]

- anonymous

ok now it makes sense.... so ow that we have the 40/8 what do we do with it?

- anonymous

You could also answer that by just taking the denominator and multiplying it by the whole number part.

- anonymous

So then we add it to the fractional part.

- anonymous

So 5 and 3/8 as a fraction is 40/8 + 3/8

- anonymous

Take the denominator. Multiply it by the whole number. Then add that to the numerator of the fractional part. That's your improper fraction.

- anonymous

43/8...?

- anonymous

Yep. So 43/8 %

- anonymous

But we want that as just a fraction, not a percent.

- anonymous

right...

- anonymous

So to turn a percent into fraction a we just multiply the denominator by 100.

- anonymous

yep and that would be 800?? because you multiply 8 x 100= 800

- anonymous

Yep.

- anonymous

So 5 and 3/8 % = 43/800

- anonymous

oh ok..

- anonymous

So now you try one.

- anonymous

ok, and i will let you know if i get it right

- anonymous

ok

- anonymous

ok, heres my problem: 8 4/5 change it into a percent: i got 44/5 then multiplied it by 100 and got 44/100... is that correct?

- anonymous

No. 5 * 100 = 500, not 100.

- anonymous

thats what i ment sorry

- anonymous

Then yes, 44/500 is correct.

- anonymous

yay! thanks! and im sure i will have more questions, so when i do, ill just ask!

- anonymous

ok

- anonymous

how do i give you a medal?

- anonymous

ok, i have another question.....

- anonymous

nevermind!

- anonymous

Sorry, I had class. To give a medal you click the give medal button. next to any of my posts..

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