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Geometric Series to Solve for Year a Resource Will Be Depleted



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 00:00UTC (8:00pm US/Eastern)Simple derivative task, no function, only values given, how the graph might look?Simplify using Geometric seriesGeometric series for this problem..?Optimizing number of production runs?Solve an geometric seriesGeometric series functionfind the annual per capita spending for personal consumption in doller?Basic Geometric SeriesStarting index for geometric series testSolve geometric series equation with large terms










0












$begingroup$


The original problem is as follows:




A community has 300 million tons of a non-renewable resource. Annual consumption is 25 million tons per year. Consumption is expected to decrease by 10% each year. Will the resource ever be depleted?




I set up the geometric series as



Total usage = 25[1 + (0.90) + (0.90)^2 + ...]
= 25[1/1-0.90]
= 250 million tons
No, the resource will not be depleted at this rate.


The second part of the problem asks:




What is the minimum percentage they can decrease consumption by to guarantee the resource does not run out?




Total usage = 25[1 + x + x^2 + ...]
= 25[1/1-x] = 300
x = 0.916
Minimum we can decrease consumption by is 8.4%


The final part of the question asks:




Suppose that it is not possible to decrease consumption of this resource by the previously given amount. The population is only able to decrease consumption by 5% each year. After how many years will the resource run out?




But I'm not exactly sure how to set this up. I'm assuming that solving for the year is just solving for n in the series where the sum up to (0.95)^n = 300, but I'm not sure how to go about setting up this equation.










share|cite|improve this question











$endgroup$
















    0












    $begingroup$


    The original problem is as follows:




    A community has 300 million tons of a non-renewable resource. Annual consumption is 25 million tons per year. Consumption is expected to decrease by 10% each year. Will the resource ever be depleted?




    I set up the geometric series as



    Total usage = 25[1 + (0.90) + (0.90)^2 + ...]
    = 25[1/1-0.90]
    = 250 million tons
    No, the resource will not be depleted at this rate.


    The second part of the problem asks:




    What is the minimum percentage they can decrease consumption by to guarantee the resource does not run out?




    Total usage = 25[1 + x + x^2 + ...]
    = 25[1/1-x] = 300
    x = 0.916
    Minimum we can decrease consumption by is 8.4%


    The final part of the question asks:




    Suppose that it is not possible to decrease consumption of this resource by the previously given amount. The population is only able to decrease consumption by 5% each year. After how many years will the resource run out?




    But I'm not exactly sure how to set this up. I'm assuming that solving for the year is just solving for n in the series where the sum up to (0.95)^n = 300, but I'm not sure how to go about setting up this equation.










    share|cite|improve this question











    $endgroup$














      0












      0








      0





      $begingroup$


      The original problem is as follows:




      A community has 300 million tons of a non-renewable resource. Annual consumption is 25 million tons per year. Consumption is expected to decrease by 10% each year. Will the resource ever be depleted?




      I set up the geometric series as



      Total usage = 25[1 + (0.90) + (0.90)^2 + ...]
      = 25[1/1-0.90]
      = 250 million tons
      No, the resource will not be depleted at this rate.


      The second part of the problem asks:




      What is the minimum percentage they can decrease consumption by to guarantee the resource does not run out?




      Total usage = 25[1 + x + x^2 + ...]
      = 25[1/1-x] = 300
      x = 0.916
      Minimum we can decrease consumption by is 8.4%


      The final part of the question asks:




      Suppose that it is not possible to decrease consumption of this resource by the previously given amount. The population is only able to decrease consumption by 5% each year. After how many years will the resource run out?




      But I'm not exactly sure how to set this up. I'm assuming that solving for the year is just solving for n in the series where the sum up to (0.95)^n = 300, but I'm not sure how to go about setting up this equation.










      share|cite|improve this question











      $endgroup$




      The original problem is as follows:




      A community has 300 million tons of a non-renewable resource. Annual consumption is 25 million tons per year. Consumption is expected to decrease by 10% each year. Will the resource ever be depleted?




      I set up the geometric series as



      Total usage = 25[1 + (0.90) + (0.90)^2 + ...]
      = 25[1/1-0.90]
      = 250 million tons
      No, the resource will not be depleted at this rate.


      The second part of the problem asks:




      What is the minimum percentage they can decrease consumption by to guarantee the resource does not run out?




      Total usage = 25[1 + x + x^2 + ...]
      = 25[1/1-x] = 300
      x = 0.916
      Minimum we can decrease consumption by is 8.4%


      The final part of the question asks:




      Suppose that it is not possible to decrease consumption of this resource by the previously given amount. The population is only able to decrease consumption by 5% each year. After how many years will the resource run out?




      But I'm not exactly sure how to set this up. I'm assuming that solving for the year is just solving for n in the series where the sum up to (0.95)^n = 300, but I'm not sure how to go about setting up this equation.







      calculus geometric-series






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Apr 1 at 19:06









      Andrei

      13.9k21330




      13.9k21330










      asked Apr 1 at 18:51









      John ProctorJohn Proctor

      31




      31




















          1 Answer
          1






          active

          oldest

          votes


















          1












          $begingroup$

          Welcome on math.stackexchange!
          For the geometric series there is not only a formula for $sum_n=0^infty q^n$ but also for the finite sums, namely
          $$
          sum_n=0^k q^n=frac1-q^k+11-q
          $$

          and this holds for $q not =1$.
          With this formula you can then calculate the year.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            Thanks, that's exactly the formula I was looking for.
            $endgroup$
            – John Proctor
            Apr 1 at 19:06










          • $begingroup$
            You're welcome.
            $endgroup$
            – Jonas Lenz
            Apr 1 at 19:07











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          1 Answer
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          active

          oldest

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          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          1












          $begingroup$

          Welcome on math.stackexchange!
          For the geometric series there is not only a formula for $sum_n=0^infty q^n$ but also for the finite sums, namely
          $$
          sum_n=0^k q^n=frac1-q^k+11-q
          $$

          and this holds for $q not =1$.
          With this formula you can then calculate the year.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            Thanks, that's exactly the formula I was looking for.
            $endgroup$
            – John Proctor
            Apr 1 at 19:06










          • $begingroup$
            You're welcome.
            $endgroup$
            – Jonas Lenz
            Apr 1 at 19:07















          1












          $begingroup$

          Welcome on math.stackexchange!
          For the geometric series there is not only a formula for $sum_n=0^infty q^n$ but also for the finite sums, namely
          $$
          sum_n=0^k q^n=frac1-q^k+11-q
          $$

          and this holds for $q not =1$.
          With this formula you can then calculate the year.






          share|cite|improve this answer









          $endgroup$












          • $begingroup$
            Thanks, that's exactly the formula I was looking for.
            $endgroup$
            – John Proctor
            Apr 1 at 19:06










          • $begingroup$
            You're welcome.
            $endgroup$
            – Jonas Lenz
            Apr 1 at 19:07













          1












          1








          1





          $begingroup$

          Welcome on math.stackexchange!
          For the geometric series there is not only a formula for $sum_n=0^infty q^n$ but also for the finite sums, namely
          $$
          sum_n=0^k q^n=frac1-q^k+11-q
          $$

          and this holds for $q not =1$.
          With this formula you can then calculate the year.






          share|cite|improve this answer









          $endgroup$



          Welcome on math.stackexchange!
          For the geometric series there is not only a formula for $sum_n=0^infty q^n$ but also for the finite sums, namely
          $$
          sum_n=0^k q^n=frac1-q^k+11-q
          $$

          and this holds for $q not =1$.
          With this formula you can then calculate the year.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Apr 1 at 18:58









          Jonas LenzJonas Lenz

          694215




          694215











          • $begingroup$
            Thanks, that's exactly the formula I was looking for.
            $endgroup$
            – John Proctor
            Apr 1 at 19:06










          • $begingroup$
            You're welcome.
            $endgroup$
            – Jonas Lenz
            Apr 1 at 19:07
















          • $begingroup$
            Thanks, that's exactly the formula I was looking for.
            $endgroup$
            – John Proctor
            Apr 1 at 19:06










          • $begingroup$
            You're welcome.
            $endgroup$
            – Jonas Lenz
            Apr 1 at 19:07















          $begingroup$
          Thanks, that's exactly the formula I was looking for.
          $endgroup$
          – John Proctor
          Apr 1 at 19:06




          $begingroup$
          Thanks, that's exactly the formula I was looking for.
          $endgroup$
          – John Proctor
          Apr 1 at 19:06












          $begingroup$
          You're welcome.
          $endgroup$
          – Jonas Lenz
          Apr 1 at 19:07




          $begingroup$
          You're welcome.
          $endgroup$
          – Jonas Lenz
          Apr 1 at 19:07

















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