Question

Please someone help me! 10 5/12 - 3 9/10. What am I doing wrong? I keep getting 6 1/30 when its suppose to be 6 31/60.

Answer 1

Showing us all your work would help us help you.

Answer 2

@mathmale
Here is my work:
(10-3)+(5/12-9/10)
LCD=2x2x3x5
LCD=4x15=60
50/60-108/60
7+(50/60-108/60)
since you cant subtract 50/60 from 108/60 properly I have to borrow from the whole 7
6(1 50/60-108/60)
1x60+50
60+50=110
6+110/60-108/60
6+2/60
6 1/30

Answer 3

@mathmale Please come back! I typed that all out for you :(

Answer 4

Ive spent way too long on this problem

Answer 5

Your LCD is 60 correct?

Answer 6

Yes

Answer 7

Isnt that right?

Answer 8

Yes. So you have to get a common denominator of 60 for both fractions, right?

Answer 9

\[\frac{ 5 }{ 12 }-\frac{ 9 }{ 10 }\] is this right?

Answer 10

Yes and then I multiply 5 by 10 and 9 by 12

Answer 11

Yes

Answer 12

Thats the original fractions

Answer 13

Oh so your denominator is going to be 120 then?

Answer 14

No...

Answer 15

I thought I only needed to multiply the top part of the fraction by the opposite bottoms

Answer 16

If you multiply the first fraction by 10 (both numerator and denominator), your denominator will be 120.

Answer 17

I tried doing that previously but my answer still came out to 6 1/30

Answer 18

When getting common denominators, you need to multiply top and bottom by the same thing or else you are changing the value of the fraction.

Answer 19

Okay well let's try it with 120 first, then we can do 60 later. Should be same answers.

Answer 20

\[\frac{ 5 }{ 12 }\times \frac{ 10 }{ 10 }\]

Answer 21

Okay so we're not finding LCD ?

Answer 22

Its 9/10 not 10/10

Answer 23

Well you already found the LCD, 60.

Answer 24

Yes but I'm multiplying by 10/10 (which is the same thing as 1) to change the denominator to 120.

Answer 25

Okay so we have the LCD now we multiply 5/12 by 10 to get 50/120 and 9/10 by 12 to get 108/120?

Answer 26

What????

Answer 27

Okay hang on a minute. So you have your LCD, 60. But where are you using that in your work?

Answer 28

Hold on Ill send a pic

Answer 29

Can you see it?

Answer 30

yup

Answer 31

Im not understanding what Im doing :(

Answer 32

Can someone go through the correct steps with me?

Answer 33

Okay I'll start from the beginning. You're getting confused on converting to the common denominator which is an easy thing to clear up :)

Answer 34

Actually, you identified the LCD correctly minutes ago.

You are subtracting 9/10 from 5/12. Can you convert these fractions so that both have the same denominator (60)?

\[\frac{ 9 }{ 10 }\frac{ 6 }{ 6 }=?\]

Answer 35

Okay so I have it written as (10-3)+(5/12-9/10) and Ive found the LCD=60, now what do I do?

Answer 36

Now you please change -9/10 so this fraction has a denom. of 60.

Answer 37

Wait, where did the 6 come from though?

Answer 38

\[\frac{ 5 }{ 12 }-\frac{ 9 }{ 10 }\]
This is your original problem. (you already subtracted the whole numbers so we don't need to worry about that part.)

Answer 39

In order to combine fractions, they need the same bottom number (common denominator).

Answer 40

Yes which is the LCD, 60 right?

Answer 41

If you are able to undrstand WHY the LCD is 60, then you can see that mult. 12 in the denom. of the first fraction by 6 will give you 60. Mult the numerator by 6 also. What do you get?

Answer 42

Yes perfect! You can really pick any number you want that both numbers are a factor of (so you could do 120 for the bottom number because 12 can go into 120 and 10 can also go into 120.) But the LCD is the easiest to work with, 60.

Answer 43

Okay so do I have 5/60-9/60 or 50/60-108/60

Answer 44

(10-3)+(5/12-9/10) is fine, great, perfect.

10-3=7, and (separately),

Combine 5/12 and -9/10.

As before, \[\frac{ 5 }{ 12}\frac{ 5 }{ 5}-\frac{ 9 }{ 10 }\frac{ ? }{ ? }\]

Answer 45

Im sorry If Im giving you guys a hard time :/ Im so confused

Answer 46

Well in order to get 60 on the denominator what do you need to multiply the first fraction's denominator by? 12x___=60

Answer 47

You must multiply 10 by what number to get 60...?

Replace the ? marks with the proper numeral:\[\frac{ 5 }{ 12}\frac{ 5 }{ 5}-\frac{ 9 }{ 10 }\frac{ ? }{ ? }\]

Answer 48

No problem! It's understandable to be confused. You'll get it :)

Answer 49

so 5/12 times 5/5 and 9/10 times 9/9?

Answer 50

and 12x_=60 is 5

Answer 51

your lcd is 60, so you would not want to multiply that denominator 10 by 9, would you?
That'd give yu 90; you want 60.

Try again.\[\frac{ 5 }{ 12}\frac{ 5 }{ 5}-\frac{ 9 }{ 10 }\frac{ ? }{ ? }\]

Answer 52

The first one is correct. To get the denominator to equal 60 you need to multiply 12 by 5. But what you do to the bottom, you must do to the top (very important rule!). So you multiply the numerator (top number) by 5 also. So what is the first "new" fraction equal to?

Answer 53

Ohh okay I see what your saying, I was too hung up on the 5 and 9 on top of the fraction its would be 9/10 time 6/6 then

Answer 54

Yup!

Answer 55

25/60 right?

Answer 56

Exactly!! How about the 2nd fraction?

Answer 57

Yes. So, your 9/10 would become 54/60.

So now you have 25/60 - 54.59, Combine these into 1 fraction.

Answer 58

Yes 54/60

Answer 59

Wait I cant do 25/60 - 54/60 though

Answer 60

I thought I have to borrow a 1 from the 7 whole number

Answer 61

Yes. Glad you found my error!

25/60-54/60 = what? Your answer MUST have the LCD 60.

What is 25-54?

Answer 62

so it would be 6+(1 25/60-54/60)

Answer 63

You combined the integers first, and got 7; now you are finishing up combining the fractions, and have (25-54)/60. Simplify that. I think you're beginning teh borrowing process too soon.

Answer 64

So I would do 1 time 25 plus 60 to get 85/60 right?

Answer 65

Let's slow down just a little bit. Please, combine 25/60 - 54/60.

Answer 66

then do 85/60-54/60 to get 6 31/60

Answer 67

Please slow down. Too early to be borrowing!

Answer 68

combine: 25/60 - 54/60.

Answer 69

Oh sorry, my teacher was having us doing borrowing in this lesson but I suppose you could subtract that to get a negetaive though

Answer 70

Too early. please combine the fractions.

Answer 71

itd be -29/60

Answer 72

Actually you did get the right answer lol

Answer 73

Yes, that's right.

Now you have 7 - 29/60.
Now you must borrow a 1, or 60/60, from that 7.

Do that now.

Answer 74

I know :) Thanks!

Answer 75

So you can borrow then if that makes it easier for you :P

Answer 76

Thank you both for the help!

Answer 77

No problem, hope it helped some!

Answer 78

Hope you'll review this problem solution so that you'll be better able to tackle the next similar problem.

Answer 79

It did tremendously! My teacher had shown us in class but I was looking at it the wrong way, thanks so much for going through it with me!

Answer 80

Ah no problem :) Good luck with the rest of your work!