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April 8th, 2015, 12:11 PM  #1 
Newbie Joined: Apr 2015 From: London Posts: 1 Thanks: 0  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. 
April 8th, 2015, 01:16 PM  #2  
Global Moderator Joined: May 2007 Posts: 6,823 Thanks: 723  Quote:
Last edited by skipjack; April 9th, 2015 at 03:21 AM.  
April 9th, 2015, 01:46 AM  #3 
Senior Member Joined: Apr 2014 From: Glasgow Posts: 2,161 Thanks: 734 Math Focus: Physics, mathematical modelling, numerical and computational solutions 
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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