Why do we need to add and subtract fractions?

Well, suppose your cooking, and you need, say, 2/3 of a cup of sugar. What if your only doing half of a recipe? You need to chop 2/3 in half. Or if your doing 2 times the recipe. You need to double 2/3. This is only one example, there are lots of others.

If you have a whole number minus a fraction for example 3 - 2 2/3 how do you do this

Think of the numbers as improper fractions. For ex: 9/3 - 8/3 = 1/3. That way all you have to do is subtract the numerators.

Why the minus sign for 3-2/5? I still don't get it.

Do you know about negative numbers? If you, then please realize - 1 (or minus one) is also a -1 (negative one).

this is hard I can't do some problems with this even though he explained it 😪😪😪😯😯😥😥 so can someone explain it much more simpilaier or easier to me?

Okay, Error. For example: 12 3/4 - 7 4/5 = ? Here, find the LCM of both the denominators. 4 and 5's LCM is 20, so it should be 12 ?/20 - 7 ?/20. Here, multiply both numerators by the number you multiplied the denominator to get to 20. Since you multiplied 4 against 5, which is 20, multiply 3 against 5, the answer to which is 12 15/20. Since you multiplied 5 against 4, which is 20, multiply 4 against 5, the answer to which is 7 16/20. Now, subtract the numbers. Here, you need to borrow 1 from 12. Borrow it, and add 20/20 to 15. You now have 12 35/20. Subtract 7 16/20 from it. 12 35/20 - 7 16/20 = 5 19/20. Voilá! You're done! #QED Hope this helps, Error.

why is fractions so important?

Fractions will become important when you get older. For example, if you are baking, you have to know what 1/2 is or 1/4.

Note that 1/3 = 4/12. So 46 1/3 - 8 7/12 = 46 4/12 - 8 7/12. This becomes 46-8=38, but with 3/12 missing. So the answer is 37 9/12, which reduces to 37 3/4. Have a blessed, wonderful day!

when do we usually use the add and subtract fraction in real life? 😕😕😕

In the previous lessons, you learned that a fraction is part of a whole. Fractions show how much you have of something, like 1/2 of a tank of gas or 1/3 of a cup of water. In real life, you might need to add or subtract fractions. For example, have you ever walked 1/2 of a mile to work and then walked another 1/2 mile back?

hello i nee lots of help i dont know how to add fractions if anyone noews the answer can someone pleaes3e tell me sporry my kat is walkijg over ny jkeayboard so i cant ytype very well its quite an issue yes. sorry for speaking bad francais i am not familiar with argentina.

Well first do 1/2+1/2 the denominator stays the same so add the 1+1 that’s 2 so the answer for that is 2/2 also known as a whole aka 1 1/3+1/5 to find a common denominator multiply the denominator that’s 15 so for 1/3 u multiply 3x5 to be 15 so u do 1x5 for the numerator for 1/5 you do 5x3 to be 15 so do 1x3 for numerator to find that. Add them up and u got your answer. I hoped this helped srry if it’s late and long!

What happens if the first number is negative and you are subtracting them? Do you have to do something different?

Yes you do. Example: -1/2 - 3/4 Since the fractions have the same sign, we add (follow me here). 1/2 = 2/4, and what is 2/4 + 3/4? 5/4, or 1 1/4. Now, since we started with two negatives, make your answer negative. -1/2 - 3/4 = - 1 1/4

Main content

Arithmetic (all content)

Course: Arithmetic (all content) > Unit 5

Lesson 16: Adding and subtracting mixed number with unlike denominators

Subtracting mixed numbers: 7 6/9 - 3 2/5

Name: Subtracting mixed numbers: 7 6/9 - 3 2/5
Uploaded: 2012-07-23T22:03:14Z
Description: We can subtract two mixed numbers, by converting them to improper fractions. First, multiply the whole number by the denominator and add the numerator to get the improper fraction. Find a common denominator and adjust the numerators accordingly. Subtract the two improper fractions, and simplify the result if possible. Finally, convert the improper fraction back to a mixed number if desired

Google Classroom

We can subtract two mixed numbers, by converting them to improper fractions. First, multiply the whole number by the denominator and add the numerator to get the improper fraction. Find a common denominator and adjust the numerators accordingly. Subtract the two improper fractions, and simplify the result if possible. Finally, convert the improper fraction back to a mixed number if desired. Created by Sal Khan.

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Ashlynne Donovan
Posted 11 years ago. Direct link to Ashlynne Donovan's post “Why do we need to add and...”
Why do we need to add and subtract fractions?
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- Testing
  Posted 11 years ago. Direct link to Testing's post “Well, suppose your cookin...”
  Well, suppose your cooking, and you need, say, 2/3 of a cup of sugar. What if your only doing half of a recipe? You need to chop 2/3 in half. Or if your doing 2 times the recipe. You need to double 2/3. This is only one example, there are lots of others.
  Comment on Testing's post “Well, suppose your cookin...”
  (75 votes)
melissa.ebener
Posted 6 years ago. Direct link to melissa.ebener's post “If you have a whole numbe...”
If you have a whole number minus a fraction for example 3 - 2 2/3 how do you do this
Button navigates to signup pageButton navigates to signup page
(13 votes)
Answer
- ethanhamza
  Posted 6 years ago. Direct link to ethanhamza's post “Think of the numbers as i...”
  Think of the numbers as improper fractions. For ex: 9/3 - 8/3 = 1/3.
  That way all you have to do is subtract the numerators.
  Button navigates to signup page
  (10 votes)
Waffles the great!
Posted 7 years ago. Direct link to Waffles the great!'s post “Why the minus sign for 3-...”
Why the minus sign for 3-2/5? I still don't get it.
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(10 votes)
Answer
- Ida Fan
  Posted 7 years ago. Direct link to Ida Fan's post “Do you know about negativ...”
  Do you know about negative numbers? If you, then please realize - 1 (or minus one) is also a -1 (negative one).
  Comment on Ida Fan's post “Do you know about negativ...”
  (8 votes)
becca
Posted 2 years ago. Direct link to becca's post “why is fractions so impor...”
why is fractions so important?
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- Amelie Cademartori
  Posted 2 years ago. Direct link to Amelie Cademartori's post “Fractions will become imp...”
  Fractions will become important when you get older. For example, if you are baking, you have to know what 1/2 is or 1/4.
  Comment on Amelie Cademartori's post “Fractions will become imp...”
  (9 votes)
error
Posted 2 years ago. Direct link to error's post “this is hard I can't do s...”
this is hard I can't do some problems with this even though he explained it 😪😪😪😯😯😥😥 so can someone explain it much more simpilaier or easier to me?
Button navigates to signup pageComment on error's post “this is hard I can't do s...”
(6 votes)
Answer
- Adrian
  Posted 2 years ago. Direct link to Adrian's post “Okay, Error. For exampl...”
  Okay, Error.
  
  For example:
  
  12 3/4 - 7 4/5 = ?
  
  Here, find the LCM of both the denominators.
  
  4 and 5's LCM is 20, so it should be 12 ?/20 - 7 ?/20.
  
  Here, multiply both numerators by the number you multiplied the denominator to get to 20.
  
  Since you multiplied 4 against 5, which is 20, multiply 3 against 5, the answer to which is 12 15/20.
  
  Since you multiplied 5 against 4, which is 20, multiply 4 against 5, the answer to which is 7 16/20.
  
  Now, subtract the numbers.
  
  Here, you need to borrow 1 from 12.
  
  Borrow it, and add 20/20 to 15. You now have 12 35/20. Subtract 7 16/20 from it.
  
  12 35/20 - 7 16/20 = 5 19/20.
  
  Voilá! You're done!
  
  #QED
  
  Hope this helps, Error.
  Comment on Adrian's post “Okay, Error. For exampl...”
  (10 votes)
Cynthia Cantillon
Posted 2 years ago. Direct link to Cynthia Cantillon's post “46 1/3 - 8 7/12 =”
46 1/3 - 8 7/12 =
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(5 votes)
Answer
- Ian Pulizzotto
  Posted 2 years ago. Direct link to Ian Pulizzotto's post “Note that 1/3 = 4/12. So...”
  Note that 1/3 = 4/12.
  
  So 46 1/3 - 8 7/12 = 46 4/12 - 8 7/12.
  
  This becomes 46-8=38, but with 3/12 missing. So the answer is 37 9/12, which reduces to 37 3/4.
  
  Have a blessed, wonderful day!
  Button navigates to signup page
  (5 votes)
chicken;)
Posted a year ago. Direct link to chicken;)'s post “i dont get it at all”
i dont get it at all
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(6 votes)
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Kien Oehlke
Posted 5 years ago. Direct link to Kien Oehlke's post “hello i nee lots of help ...”
hello i nee lots of help i dont know how to add fractions if anyone noews the answer can someone pleaes3e tell me sporry my kat is walkijg over ny jkeayboard so i cant ytype very well its quite an issue yes. sorry for speaking bad francais i am not familiar with argentina.
Button navigates to signup pageButton navigates to signup page
(2 votes)
Answer
- Adyasha_Priyadarsini
  Posted a year ago. Direct link to Adyasha_Priyadarsini's post “Well first do 1/2+1/2 the...”
  Well first do 1/2+1/2 the denominator stays the same so add the 1+1 that’s 2 so the answer for that is 2/2 also known as a whole aka 1
  
  1/3+1/5 to find a common denominator multiply the denominator that’s 15 so for 1/3 u multiply 3x5 to be 15 so u do 1x5 for the numerator for 1/5 you do 5x3 to be 15 so do 1x3 for numerator to find that. Add them up and u got your answer.
  
  I hoped this helped srry if it’s late and long!
  Comment on Adyasha_Priyadarsini's post “Well first do 1/2+1/2 the...”
  (3 votes)
Iam_Avery
Posted 2 years ago. Direct link to Iam_Avery's post “when do we usually use th...”
when do we usually use the add and subtract fraction in real life?
😕😕😕
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- Woah
  Posted 2 years ago. Direct link to Woah's post “In the previous lessons, ...”
  In the previous lessons, you learned that a fraction is part of a whole. Fractions show how much you have of something, like 1/2 of a tank of gas or 1/3 of a cup of water. In real life, you might need to add or subtract fractions. For example, have you ever walked 1/2 of a mile to work and then walked another 1/2 mile back?
  Comment on Woah's post “In the previous lessons, ...”
  (4 votes)
.
Posted 7 years ago. Direct link to .'s post “What happens if the first...”
What happens if the first number is negative and you are subtracting them? Do you have to do something different?
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(2 votes)
Answer
- Ida Fan
  Posted 7 years ago. Direct link to Ida Fan's post “Yes you do. Example: -1/2...”
  Yes you do. Example: -1/2 - 3/4
  Since the fractions have the same sign, we add (follow me here). 1/2 = 2/4, and what is 2/4 + 3/4? 5/4, or 1 1/4.
  Now, since we started with two negatives, make your answer negative.
  -1/2 - 3/4 = - 1 1/4
  Comment on Ida Fan's post “Yes you do. Example: -1/2...”
  (8 votes)

Video transcript

Let's try to evaluate 7 and 6/9 minus 3 and 2/5. So like always, I like to separate out the whole number parts from the fractional parts. This is the same thing as 7 plus 6/9 minus 3 minus 2/5. And the reason why I'm saying minus 3 minus 2/5 is this is the same thing as minus 3 plus 2/5. And so you distribute the negative sign. You're subtracting a 3, and then you're subtracting the 2/5. And so now we can worry about the whole number parts, 7 minus 3. Well, 7 minus 3 is going to give us 4. So that's going to give us 4. And then we're going to have 6/9 minus 2/5. So let me think about what 6/9 minus 2/5 are. 6/9 minus 2/5, well, we're going to have to find a common denominator. So this is going to be the same thing. And I think the least common multiple of 9 and 5 is going to be 45. Literally, you then multiply. They have no common factors. So it's going to be over 45. To go from 9 to 45, I have to multiply by 5. So I'm going to have to multiply the numerator by 5. So 6 times 5 is 30. Then I'm going to subtract. To go from 5 to 45, I had to multiply by 9. So I have to multiply the numerator by 9 if I don't want to change the value. So 2 times 9 is 18. And 30/45 minus 18/45 is going to be something over 45. 30 minus 18 is 12. If I subtract these two fractions right over here, I get 12/45. So it's 4 plus 12/45. Or if we wanted to write it as a mixed number, this is equal to 4 and 12/45. But we're not done yet. We can simplify this further. 12 and 45 have common factors. They're both divisible by 3. Actually, they're both divisible by-- well, I think we can divide more after that. So let's see. If we divide the numerator by 3 and the denominator by 3, we end up with 4. And 12 divided by 3 is 4. And 45 divided by 3 is 15. 4 and 4/15. And actually, we're done. These two can't be simplified anymore. 4 and 4/15.