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Figuring with percents

  1. Mar 26, 2008 #1
    1. The problem statement, all variables and given/known data

    Bottled water consumption was reported to be 21 gal per person in the United States in 2002. The last census reported 2.9 x 10^8 people in the U.S.
    A. What is the total estimated bottled water consumption in the U.S.?
    B. If the per capita consumption of bottled water has increased 20% in the last 10 years, what was the per capita consumption 10 years ago?

    3. The attempt at a solution

    A. 290,000,000 (or 2.9x10^8) x 21 gal = 6,090,000,000 (or 6.09x10^9)
    B. 20% of 21 gallons is 4.2 gallons. Do I add or subtract that from the 21 gal? How do I figure what the per capita consumption was 10 years ago?
  2. jcsd
  3. Mar 27, 2008 #2


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    Be careful. Saying that the consumption has increased 20% from 1992 means that it has increased by 20% of the consumption in 1992- and we don't know what that was! If we let C= consumption in 1992, then "increasing 20%" means it increased by 0.20C. The consumption in 2002 would be the consumption in 1992 plus the increase: C+ .20C= 1.20C. Since you are told that the consumption in 2002 was 21 gallons per person, 1.20C= 21. Solve that for C to find the per capita consumption in 1992.
  4. Mar 27, 2008 #3
    Wow, I am amazed at the number of posts you have done:) I think that is the most I have seen!! Ok, on to my problem...Thanks for explaining this problem in depth. I had wondered if the 10 years ago was from the 2002 or not, so thanks for pointing which one is was out. To figure out what the per capita consumption in 1992 was, I divided 21 by 1.20C. I got 17.5. Did I use the correct formula? Does this answer make sense? thanks
  5. Mar 27, 2008 #4


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    I hope you mean that you divided 21 by 1.2 and got C= 17.5 gallons of bottled water consumed per capita in 1992.
  6. Mar 27, 2008 #5
    Sorry that I did not write my 17.5 in a complete sentance! Yes, I did mean 17.5 gallons of bottled water consumed per capita in 1992.
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