1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about percentage

  1. Mar 15, 2012 #1
    I'm trying to understand this problem.

    If a lollipop costed $6 and now it costs $8, how much percent the price grow?

    I think the answer is ((8-6)/8)*100=25%

    So I'm trying to apply this solution to the new problem. If a lollipop costed $1, and now it costs $2, how much percent the price grow?
    ((2-1)/2)*100=50%, but it should be 100%.

    Can anyone help me with this problems?
     
  2. jcsd
  3. Mar 15, 2012 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    I think you already know the answer: what must be in the denominator in order that your second example gives you 100%?

    RGV
     
  4. Mar 15, 2012 #3
    In the denominator should be 1. But in the first equation it should be 8. This is the part that I don't get it. I'm putting in the denominator the current price.
     
  5. Mar 15, 2012 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    I understand what you are doing. I don't understand *why* you are doing it differently in the two examples.

    RGV
     
  6. Mar 15, 2012 #5

    Mark44

    Staff: Mentor

    The denominator should have the price we're calculating the percent increase/decrease for.

    For your two examples, the starting prices were $6 and $1, respectively, so those are the numbers you need to use in the denominator.

    On the other hand, if the price of something goes down from from $10 to $8, then the percent decrease is (10 - 8)/10 * 100 = 20 %.

    If the price happened to go back up by $2, then the percent increase would be (10 - 8)/8 * 100 = 25%. The reason we're getting a different number is we're using a different base or starting point.
     
  7. Mar 15, 2012 #6
    I wasn't understanding the problem because I got different percentage values. In the example of Mark44 the same price decreased 20% to pass from $10 to $8, and the increased 25% to pass from $8 to $10. Projecting my question with Mark 44 explanation, my confusion was in the different percentage values. I was thinking why a price decreases 20%, and it has to increase 25%, and not 20%, to get to the initial value? Now, I understand.
     
  8. Mar 15, 2012 #7
    [itex]\frac{new-old}{old}[/itex](100)

    Because the amount you're multiplying the percent by is smaller.
     
  9. Mar 15, 2012 #8

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    That's because the answer you gave to the first problem is wrong. If the lollypop increased from 6$ to 8$ then it increased by $2 and that is 2/6= 1/3 of the original price. The price of the lollypop increased by 1/3 or 33 and 1/3 percent, NOT 25%.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question about percentage
  1. Percentage question (Replies: 7)

Loading...