Question

find the LCD for 3/7+1/3. explain

Answer 1

i dont really know what can be divisible for 7 and 3 besides 1

Answer 2

?

Answer 3

http://www.mathsisfun.com/least-common-denominator.html

Answer 4

LCD is basically like LCM of denominators.

Answer 5

So what is LCM of 3 and 7?

Answer 6

thats alot of reading...

Answer 7

hmm

Answer 8

idrk cause nothing is really divisible

Answer 9

LCM = least common multiple

Answer 10

i know that but i dont get how to find that out for 7 and 3

Answer 11

What is prime factorization of 3?

What about 7?

Answer 12

nothing can go into 3 or 7 besides 1

Answer 13

Right, so 3 and 7 are both prime, right?

Answer 14

yeah

Answer 15

So to find LCM of primes number, you just multiple them together.

Answer 16

So \(LCM(3,7)=3\times7\)

Answer 17

so it would be 3/21?

Answer 18

\(3\times7 = 21\). That tells us that denominator need to be 21, right?

In \(\dfrac{3}{7}\), we need denominator to be 21. What to do?

Answer 19

cause it has to be a number, euh 3x7?

Answer 20

well, to get from \(7\) to \(21\), we multiply it by \(3\), right?

But because we did something in denominator, we must do same to numerator.

So we have \(\dfrac{3}{7}\rightarrow\dfrac{3\times3}{7\times3} = \dfrac{9}{21}\).

Makes sense?

Can you do that for 1/3 ?

Answer 21

hmmm 1/3? wouldnt it be the same?

Answer 22

Well, to add fraction together, we need denominator to be same, so we need to rewrite 1/3.

Answer 23

hmm rewrite 1/3. that sounds confusing

Answer 24

rewrite 1/3 means write it again, so it is same thing, but look different.

Answer 25

Like for 1/2, we can rewrite it as 2/4, or 4/8

Answer 26

ohh let me try

Answer 27

Alright, denominator just need to be 21.

Answer 28

hmm...

Answer 29

So we need \(\dfrac{1}{3}~\rightarrow~\dfrac{?}{21}\)

Answer 30

7/21?

Answer 31

What to do with denominator and numerator?

Answer 32

Yes

Answer 33

@gorv

Answer 34

oh so its 7/21?

Answer 35

So we now have \(\dfrac{3}{7}+\dfrac{1}{3}\rightarrow\dfrac{9}{21}+\dfrac{7}{21}\).

Now we can add fractions.

Answer 36

so 9/21 + 7/21?

Answer 37

yeah

Answer 38

which is 16/21?

Answer 39

yeah that is right

Answer 40

greeky42 guided u well

Answer 41

lol yeah @geerky42 did

Answer 42

lol thanks, so do you understand what we did so far?

Answer 43

grrr it has to be a single digit number, but yeah i kinda understand it

Answer 44

how do i get one number?

Answer 45

nvm i got it

Answer 46

but i have a few more

Answer 47

hold on