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Homework Help: Math percent increase problem

  1. Oct 21, 2005 #1
    Can someone explain to me the following:
    If a number increases from 108,7 to 113,7 how much in percent has it increased?

    First I tried to do 108,7 / 113,7 = 0,956.
    1 - 0,956 = 0,0439. In other words, an increase of 4,39%. This turns out to be wrong. 113,7 / 108,7 = 1,0459 -> an increase of 4,59% is correct, but I fail to see the logic in that the last approach is correct. What am I actually calculating in my first try?
     
  2. jcsd
  3. Oct 21, 2005 #2
    In your first try you're finding that 108.7 is 0.956*100 = 95.6% out of 113.7.

    Look at the increase from 108.7 to 113.7, it's a increase by 5 units. (113.7-108.7). Now, if we want to find how many % 5 is out of 108.7, we do (5/108.7)*100 = 4.59%. So, in general:
    If a number increases from a to b, how many percent did it increase?
    Answer:
    [(b-a)/a]*100%
     
  4. Oct 21, 2005 #3
    Aha, thanks alot Karlsen!
     
  5. Oct 21, 2005 #4
    Always nice to help a fellow citizen.
     
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