Help subtracting these fractions please

  • #1
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Homework Statement:

Subtracting mixed numbers

Relevant Equations:

Least common multiple
104001795_188426312532985_465687906107087136_n.jpg



I really can t find my mistake here 17/20 is the proper answer

Thanks
 
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Answers and Replies

  • #2
berkeman
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When you put the 3 fractions over the common denominator of 20, it looks like you did not convert the numerators correctly.

First step is to put the front whole number of each quantity into the numerator of each fraction without changing the denominator yet. So ##5\frac{3}{4} = \frac{?}{4}##

Then after you have converted each of the 3 quantities to pure fractions, go ahead and multiply to put them over the common denominator of 20. Does that work for you?
 
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  • #3
DaveC426913
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[ DUPE ]
 
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  • #5
DaveC426913
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Heh. I was commenting on what appears to be a different error: -3/20 magically becoming 17/20.

But I see what the OP is doing. He's actually doing 1 plus -3/20, which does equal 17/20.

The OP is trying to solve the problem by splitting the number into whole and fractions and dealing with them separately:

= (5 -1 -3) + (3/4 -2/5 -1/2)

= 1 + (etc.)


This actually does result in the right answer (and frankly, it's easier math).
 
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  • #6
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When you put the 3 fractions over the common denominator of 20, it looks like you did not convert the numerators correctly.

First step is to put the front whole number of each quantity into the numerator of each fraction without changing the denominator yet. So ##5\frac{3}{4} = \frac{?}{4}##

Then after you have converted each of the 3 quantities to pure fractions, go ahead and multiply to put them over the common denominator of 20. Does that work for you?
I will try to understand it like you are showing me , thanks
 
  • #8
161
21
When you put the 3 fractions over the common denominator of 20, it looks like you did not convert the numerators correctly.

First step is to put the front whole number of each quantity into the numerator of each fraction without changing the denominator yet. So ##5\frac{3}{4} = \frac{?}{4}##

Then after you have converted each of the 3 quantities to pure fractions, go ahead and multiply to put them over the common denominator of 20. Does that work for you?
First step is to put the front whole number of each quantity into the numerator of each fraction ? can you tell how please ?
 
  • #9
DaveC426913
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First step is to put the front whole number of each quantity into the numerator of each fraction ? can you tell how please ?
Let's start simply.

For the number 1 1/2, what would that be as a fraction only? How many halves are there in and and a half?
 
  • #10
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if you can post a picture with a written work like mine should help me better thanks
 
  • #11
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Let's start simply.

For the number 1 1/2, what would that be as a fraction only? How many halves are there in and and a half?
3/2 ?
 
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  • #12
DaveC426913
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if you can post a picture with a written work like mine should help me better thanks
Sorry. You're supposed to do the work, not us.
 
  • #17
DaveC426913
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Perfect. Now the other two in your problem.
 
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  • #18
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Perfect. Now the other two in your problem.
7/5 oh so my mistake was that i was making /20 ?
 
  • #19
DaveC426913
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7/5 oh so my mistake was that i was making /20 ?
You're gonna do that next.

Show all your work so far.
 
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  • #20
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103965114_268599944211570_3451833833866637948_n.jpg
 
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  • #22
berkeman
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Yes, now put them over the common denominator of 20, do the resulting subtraction, and you have the correct answer! :smile:
 
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  • #23
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Yes, now put them over the common denominator of 20, do the resulting subtraction, and you have the correct answer! :smile:
don t ask me why but I tried this already but somehow had different answer so I gave up:smile:
well thank you all
 
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  • #24
Ibix
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don t ask me why but I tried this already but somehow had different answer so I gave up:smile:
well thank you all
It's very, very easy to make mistakes with this kind of work, no matter how experienced you are. If you think you know how to do something but get the wrong answer, turn the page and try again. There's a fair chance you just wrote a number wrong somewhere...
 
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  • #25
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Yes, now put them over the common denominator of 20, do the resulting subtraction, and you have the correct answer! :smile:

103990510_3003009179790628_1792936299955737460_n.jpg


The thing is that here it worked out without make them as fractions
 

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