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Percentages from/to negative integers
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WhytheQ
science forum beginner


Joined: 07 Jul 2006
Posts: 4

PostPosted: Fri Jul 07, 2006 8:55 am    Post subject: Percentages from/to negative integers Reply with quote

What is the fool-proof (i.e for me) formula for calculating a
percentage change.
The change will be from A to B, where the following are possibilities:

A can be positive or negative
B can be positive or negative
A can be greater than B
B can be greater than A
(if A is zero then, for practical reasons, I not interested.)

Initially I thought the formula was:
((B-A)/A)*100

but if, for example, A= -100 B= -200 then the above comes up with +100%
which doesn't make much sense.

any help greatly appreciated
Jason.
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William Elliot
science forum Guru


Joined: 24 Mar 2005
Posts: 1906

PostPosted: Fri Jul 07, 2006 9:05 am    Post subject: Re: Percentages from/to negative integers Reply with quote

On Fri, 7 Jul 2006, WhytheQ wrote:

Quote:
What is the fool-proof (i.e for me) formula for calculating a
percentage change.
The change will be from A to B, where the following are possibilities:

A can be positive or negative
B can be positive or negative
A can be greater than B
B can be greater than A
(if A is zero then, for practical reasons, I not interested.)

Initially I thought the formula was:
((B-A)/A)*100

but if, for example, A= -100 B= -200 then the above comes up with +100%
which doesn't make much sense.

It says, b is twice as much as a, which it is.

If you add 100% of a to a, you add all of a to a, ie 2a = -200 = b.

If b = 100 and a = -100, then the formula gives -200%.
If you subtract 200% of a from a you get a - 2a = -a = --100 = 100 = b.

Quote:
any help greatly appreciated
Jason.

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drmwecker@gmail.com
science forum beginner


Joined: 27 Nov 2005
Posts: 5

PostPosted: Sat Jul 08, 2006 1:12 pm    Post subject: Re: Percentages from/to negative integers Reply with quote

Actually, it's

(B-A)/A

which fraction you convert to a percentage.

It is NOT (B-A)/A * 100;
it IS (B-A)/A * 100%

This dropping of the percent sign is one of those irritating pieces of
sloppiness that is in so many texts today.

Best, Mike
DrMWEcker at aol dot com
Michael W. Ecker, Ph.D.
Assoc. Prof., PSU Wilkes-Barre
===========================

WhytheQ wrote:
Quote:
What is the fool-proof (i.e for me) formula for calculating a
percentage change.
The change will be from A to B, where the following are possibilities:

A can be positive or negative
B can be positive or negative
A can be greater than B
B can be greater than A
(if A is zero then, for practical reasons, I not interested.)

Initially I thought the formula was:
((B-A)/A)*100

but if, for example, A= -100 B= -200 then the above comes up with +100%
which doesn't make much sense.

any help greatly appreciated
Jason.
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WhytheQ
science forum beginner


Joined: 07 Jul 2006
Posts: 4

PostPosted: Sat Jul 08, 2006 3:09 pm    Post subject: Re: Percentages from/to negative integers Reply with quote

if I owed someone 100 previously, and now i owe them 200, then
saying my situation has improved 100% doesn't make much sense.

Jason



drmwecker@gmail.com wrote:

Quote:
Actually, it's

(B-A)/A

which fraction you convert to a percentage.

It is NOT (B-A)/A * 100;
it IS (B-A)/A * 100%

This dropping of the percent sign is one of those irritating pieces of
sloppiness that is in so many texts today.

Best, Mike
DrMWEcker at aol dot com
Michael W. Ecker, Ph.D.
Assoc. Prof., PSU Wilkes-Barre
==========================
WhytheQ wrote:
What is the fool-proof (i.e for me) formula for calculating a
percentage change.
The change will be from A to B, where the following are possibilities:

A can be positive or negative
B can be positive or negative
A can be greater than B
B can be greater than A
(if A is zero then, for practical reasons, I not interested.)

Initially I thought the formula was:
((B-A)/A)*100

but if, for example, A= -100 B= -200 then the above comes up with +100%
which doesn't make much sense.

any help greatly appreciated
Jason.
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