Finding Percentage of Increase

Date: 06/07/2003 at 23:03:06
From: Chief
Subject: Percentage increase

Find the percentage increase: old, $50.50; new $75.75.

Date: 06/08/2003 at 01:28:55
From: Doctor Mike
Subject: Re: Percentage increase

Hello,
  
You first figure out the amount of increase. That is 75.75 minus 
50.50, which is 25.25.
  
When you deal with percentages, you compare the increase with the 
original, which in your case is 50.50.  (original = old)
  
For me, it has always been easier to understand this comparison step 
by putting it in terms of a fraction before doing the percentage 
version of the answer. The fraction is 

     increase 
    ----------
      before
  
For this problem, the numbers for it are

     25.25 
    -------
     50.50  
  
This turns out to be exactly 0.5 or 1/2.
  
Finally, the percentage is the fraction multiplied by 100.  100 times 
0.5 is 50, so the answer is 50 percent.  
   
Put into words, it is a 50 percent increase to go from 50.50 to 75.75.  
  
Here is a similar problem where the numbers involved are easier. You 
should do the work to convince yourself that it is also a 50% increase 
to go from 50 to 75.  You are adding 25 (half of 50 = 50 percent of 
50) to get from 50 to 75. See? Good!   
  
Here is another useful related example. If you go from 50 to 100 you 
double the amount. That is, you add 100% of the original to get the 
new. This is a 100% increase.

- Doctor Mike, The Math Forum
  http://mathforum.org/dr.math/