My Math Forum  

Go Back   My Math Forum > High School Math Forum > Elementary Math

Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

LinkBack Thread Tools Display Modes
November 17th, 2018, 09:10 AM   #1
Joined: Nov 2018
From: UK

Posts: 1
Thanks: 0

Calculating percentages

Hi, I have an issue calculating these percentages.

I have a spreadsheet that applies a rate of 18 % to a figure and then an additional 20 % to the total.

I am trying to create a spreadsheet that will take a total figure and miss 20 % then an additional 18 % to give me my initial figure but the calculation is different.

Here's an example:

MaxBid = £350.00
MaxBid18 = £413.00 My formula =(MaxBid + (18/100*MaxBid)
WithVAT20 = £495.60 My formula =(MaxBid18 + (20/100*Max Bid18)

So far this seems correct to me...

Now I try to reverse engineer this calculation to give me a figure to a MaxBid:

WithVAT20 = £495.60
Minus20 = £495.60 - (20/100*£495.60) = £396.48
Minus18 = ....

However I can see I not getting the same result as before.

Can someone please correct me?



Last edited by skipjack; November 17th, 2018 at 11:52 AM.
kmorr is offline  
November 17th, 2018, 12:07 PM   #2
Global Moderator
Joined: Dec 2006

Posts: 19,986
Thanks: 1853

MaxBid + (18/100*MaxBid) = MaxBid * (1 + 0.1 = MaxBid * 1.18, so the calculation to reverse engineer this is MaxBid = MaxBid18 / 1.18, and (similarly) the calculation to reverse engineer the VAT should be MaxBid18 = WithVAT20 / 1.2.

Note that adding a percentage to a price might also involve rounding the result, and then reversing the calculation might not give precisely the original amount.
skipjack is offline  

  My Math Forum > High School Math Forum > Elementary Math

calculating, percentages

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
Percentages problem need help adding percentages please BellEnd Elementary Math 4 May 25th, 2012 02:56 PM
can someone help with percentages? yac_x Algebra 1 May 18th, 2010 03:01 PM
Percentages? jeffgothro Elementary Math 11 October 31st, 2009 04:05 AM
Percentages: cafegurl Elementary Math 6 July 26th, 2009 11:20 PM
More on Percentages. jloffredo Elementary Math 2 January 13th, 2009 07:58 PM

Copyright © 2018 My Math Forum. All rights reserved.