Question

how do i find the LCD?

Answer 1

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.

Answer 2

For example:

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

Answer 3

The other method involves factorizing your denominator

Answer 4

And is often a bit faster.

Answer 5

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

Answer 6

Yeah, that's when factorizing helps.

What are the factors of 220?

Answer 7

how do you find the factors?

Answer 8

22 * 10 = 220
(11*2)*(5*2) = 220

So the factors of 220 are 2*2*5*11

Answer 9

oh, ok thanks!!

Answer 10

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

Answer 11

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

Answer 12

So now, what are the factors of 100?

Answer 13

Pick two numbers you can multiply to get 100

Answer 14

hold up one second

Answer 15

ten and one??

Answer 16

ten times one is ten.

Answer 17

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

Answer 18

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

Answer 19

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

Answer 20

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

Answer 21

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

Answer 22

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

Answer 23

So the factors of 100 are?

Answer 24

10?

Answer 25

No. 2*2*5*5

Answer 26

sorry, like i said, a bit rusty

Answer 27

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

Answer 28

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

Answer 29

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

Answer 30

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

Answer 31

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

Answer 32

No, that's the LCF

Answer 33

ok so whats the LCD then?

Answer 34

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

Answer 35

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

Answer 36

What is 11 * 100?

Answer 37

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

Answer 38

100= 2*2 * 5*5
220= 2*2 * 5 * 11

Sorry I meant denominator

Answer 39

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

Answer 40

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

Answer 41

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

Answer 42

Do you see that?

Answer 43

yep i do!

Answer 44

Ok, so we have to make them the same

Answer 45

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.

Answer 46

oh ok!

Answer 47

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

Answer 48

1100

Answer 49

yep.

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

Answer 50

ok lets see, how about, 95 and 100

Answer 51

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

Answer 52

yep and its 10x10

Answer 53

No, you can factor that further remember?

Answer 54

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

Answer 55

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

Answer 56

anyways, do go on...

Answer 57

Ok, so factor 95

Answer 58

ok 5x19 is one i know

Answer 59

but i cant think of any others

Answer 60

That's good. There are no others.

Answer 61

oh ok

Answer 62

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.

Answer 63

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

Answer 64

Ok, which ones do they not have in common?

Answer 65

19 and 2

Answer 66

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

Answer 67

not really sure....

Answer 68

100 has all the ones 95 has except?

Answer 69

19

Answer 70

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

Answer 71

2

Answer 72

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

Answer 73

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

Answer 74

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

Answer 75

And they should be the same.

Answer 76

and it would equal to 1900

Answer 77

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

Answer 78

it equals the same, 1900

Answer 79

Yep, that's your LCD

Answer 80

Ok try another one on your own.

Answer 81

i will! thanks for all your help!!

Answer 82

Any time =)

Answer 83

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

Answer 84

Very welcome! =)

Answer 85

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

Answer 86

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

Answer 87

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

Answer 88

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

Answer 89

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

Answer 90

for example, 5 3/8 percent into a fraction

Answer 91

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

Answer 92

Basically ignore the percent for now.

Answer 93

ok hold up

Answer 94

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

Answer 95

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

Answer 96

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

Answer 97

Then add it to the 3

Answer 98

sorry, i dont know what that is