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April 8th, 2015, 12:11 PM   #1
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Set Percentage then a set figure

Hi,

I am completely useless as maths, so I know this forum is my haven!

Basically, I use a software which allows me to automatically increase a price from one source to another source based on a % increase from the original price.

My problem is probably very easy to answer; basically, I have 2 percentages to add and then a set £0.20, so for example:

7% + 3.4% = 10.4% + 20p, but I need this to be in one % of the original figure, is this possible?

Many thanks in advance.

Last edited by skipjack; April 9th, 2015 at 03:20 AM.
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April 8th, 2015, 01:16 PM   #2
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Quote:
Originally Posted by medievil2003 View Post
Hi,

I am completely useless as maths, so I know this forum is my haven!

Basically, I use a software which allows me to automatically increase a price from one source to another source based on a % increase from the original price.

My problem is probably very easy to answer; basically, I have 2 percentages to add and then a set £0.20, so for example:

7% + 3.4% = 10.4% + 20p, but I need this to be in one % of the original figure, is this possible?

Many thanks in advance.
Yes, as long as you know the original price.

Last edited by skipjack; April 9th, 2015 at 03:21 AM.
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April 9th, 2015, 01:46 AM   #3
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How's your algebra? An algebraic function describing what you stated is:

$\displaystyle P_{new} = \left(1+ \frac{p_i}{100\%}\right)P_{old} + P_{add}$

where

$\displaystyle P_{new}$ = new price of item
$\displaystyle P_{old}$ = old/original price of item

$\displaystyle p_i$ = percentage increase (e.g. 15%)
$\displaystyle P_{add}$ = price to add

Then the net percentage increase after the operation above is given by

$\displaystyle p_{net} = \left(\frac{P_{new}}{P_{old}} - 1\right) \times 100 \%$


For example, using the numbers you gave...

$\displaystyle p_i = 10.4\%$
$\displaystyle P_{add} = 20$p

and some old price... let's say $\displaystyle P_{old} = 80$p

$\displaystyle P_{new} = \left(1+ \frac{10.4\%}{100\%}\right)\times 80 + 20$
$\displaystyle = (1.104 \times 80) + 20$
$\displaystyle = 108.32$p

We can now calculate the net percentage increase:

$\displaystyle p_{net} = \left(\frac{108.32}{80} - 1\right) \times 100\%$
$\displaystyle =(1.354 - 1) \times 100 \%$
$\displaystyle = 35.4\%$

Last edited by Benit13; April 9th, 2015 at 01:56 AM.
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