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thetraveller98
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hi could someone clarifiy if this is the equation to find percentage difference:
(difference/one value)x100
that is how my teacher said we should calculate it
but on the internet there are a few other ways and now i am confused which one i should use for my controlled assessment.

btw i have the c/a on monday so it would be great to get an answer as soon as possible
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Stonebridge
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(Original post by thetraveller98)
hi could someone clarifiy if this is the equation to find percentage difference:
(difference/one value)x100
that is how my teacher said we should calculate it
but on the internet there are a few other ways and now i am confused which one i should use for my controlled assessment.

btw i have the c/a on monday so it would be great to get an answer as soon as possible
There will be variations.
If you have two values, say A and B and you want the %age difference, the obvious question is, "as a %age of what?".

Let's say B is the larger value, then
If you do
\frac{100(B-A)}{B}
then you have the difference as a %age of B
If you do
\frac{100(B-A)}{A}
then you have the difference as a %age of A

Both are correct. It usually doesn't matter unless you are specifically asked for one or the other.

There is a 3rd alternative where you could take the %age difference as a %age of the mean value of A and B.
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thetraveller98
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(Original post by Stonebridge)
There will be variations.
If you have two values, say A and B and you want the %age difference, the obvious question is, "as a %age of what?".

Let's say B is the larger value, then
If you do
\frac{100(B-A)}{B}
then you have the difference as a %age of B
If you do
\frac{100(B-A)}{A}
then you have the difference as a %age of A

Both are correct. It usually doesn't matter unless you are specifically asked for one or the other.

There is a 3rd alternative where you could take the %age difference as a %age of the mean value of A and B.
thanks a lot that makes much more sense now. could you please explain to me how you would calculate percentage error if you know how to
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Stonebridge
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(Original post by thetraveller98)
thanks a lot that makes much more sense now. could you please explain to me how you would calculate percentage error if you know how to
%age error is taken as a %age of the measured value.

If you measure a length, say, as 100mm and you have an error (uncertainty) of ±5mm then the %age error (uncertainty) is

100 \frac{(error)}{(value)}

In this case

100\frac{(±5)}{(100)}

which is ±5%

If this is not what you mean you need to explain your question in more detail or give an example of what it is you don't understand. Otherwise we're guessing what it is you want to know.
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thetraveller98
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(Original post by Stonebridge)
%age error is taken as a %age of the measured value.

If you measure a length, say, as 100mm and you have an error (uncertainty) of ±5mm then the %age error (uncertainty) is

100 \frac{(error)}{(value)}

In this case

100\frac{(±5)}{(100)}

which is ±5%

If this is not what you mean you need to explain your question in more detail or give an example of what it is you don't understand. Otherwise we're guessing what it is you want to know.
you explained it perfectly thank you so much
what i didnt know was that percentage error is the same as percentage uncertainty so thank you for clarifiying that for me.
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Stonebridge
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(Original post by thetraveller98)
you explained it perfectly thank you so much
what i didnt know was that percentage error is the same as percentage uncertainty so thank you for clarifiying that for me.
Uncertainty is probably the better word for it. "Error" makes it sound like some sort of mistake, when in fact it's really an inevitabe part of any measurement.
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thetraveller98
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(Original post by Stonebridge)
Uncertainty is probably the better word for it. "Error" makes it sound like some sort of mistake, when in fact it's really an inevitabe part of any measurement.
Thank you very much for your help
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