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In 1991, the moose population in a park was measured to be 4,360. By 1999, the population was measured again to be 5,880. Assume the population continues to change linearly.

  1. Find a formula for the moose population, P since 1990.
  2. What does your model predict the moose population to be in 2003?
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In 2003, the owl population in a park was measured to be 340. By 2007, the population was measured again to be 285. The population changes linearly. Let the input be years since 1990.

  1. Find a formula for the owl population, P . Let the input be years since 2003.
  2. What does your model predict the owl population to be in 2012?
  1. Ordered pairs are  ( 0 , 340 )  and  ( 4 , 285 ) m = 285 340 4 0 = 13.75  and  ( 0 , 340 ) y = m x + b y = −13.75 x + 340  or  P ( t ) = −13.75 t + 340
  2. The year 2012 corresponds to t = 9 P ( 9 ) = −13.75 ( 9 ) + 340 = 216.25  or 216 owls
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The Federal Helium Reserve held about 16 billion cubic feet of helium in 2010 and is being depleted by about 2.1 billion cubic feet each year.

  1. Give a linear equation for the remaining federal helium reserves, R , in terms of t , the number of years since 2010.
  2. In 2015, what will the helium reserves be?
  3. If the rate of depletion doesn’t change, in what year will the Federal Helium Reserve be depleted?
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Suppose the world’s oil reserves in 2014 are 1,820 billion barrels. If, on average, the total reserves are decreasing by 25 billion barrels of oil each year:

  1. Give a linear equation for the remaining oil reserves, R , in terms of t , the number of years since now.
  2. Seven years from now, what will the oil reserves be?
  3. If the rate at which the reserves are decreasing is constant, when will the world’s oil reserves be depleted?
  1. The year 2014 corresponds to t = 0 . We have  m = −25  and  ( 0 , 1820 ) y = m x + b y = 25 x + 1820  or  R ( t ) = −25 t + 1820
  2. R ( 7 ) = −25 ( 7 ) + 1820 = 645 billion cubic feet
  3. 0 = −25 t + 1820 −1820 = −25 t 72.8 = t  2014 + 72 .8 = 2086 .8 . So, in the year 2086
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You are choosing between two different prepaid cell phone plans. The first plan charges a rate of 26 cents per minute. The second plan charges a monthly fee of $19.95 plus 11 cents per minute. How many minutes would you have to use in a month in order for the second plan to be preferable?

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You are choosing between two different window washing companies. The first charges $5 per window. The second charges a base fee of $40 plus $3 per window. How many windows would you need to have for the second company to be preferable?

Plan 1:  y = 5 x  where x is number of windows Plan 2:  y = 3 x + 40  where x is number of windows 3 x + 40 5 x 40 2 x 20 x So, more than 20 windows
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When hired at a new job selling jewelry, you are given two pay options:

Option A: Base salary of $17,000 a year with a commission of 12% of your sales

Option B: Base salary of $20,000 a year with a commission of 5% of your sales

How much jewelry would you need to sell for option A to produce a larger income?

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When hired at a new job selling electronics, you are given two pay options:

Option A: Base salary of $14,000 a year with a commission of 10% of your sales

Option B: Base salary of $19,000 a year with a commission of 4% of your sales

How much electronics would you need to sell for option A to produce a larger income?

Option A:  y = 0.10 x  + 14,000 where  x  is dollars of sales . Option B:  y = 0.04 x + 19 , 000  where  x  is dollars of sales 0 .10 x + 14 , 000 0.04 x + 19 , 000 0.06 x + 14 , 000 19 , 000 0.06 x 5 , 000 x 83 , 333.33 So, more than $83,333 .33 in sales
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When hired at a new job selling electronics, you are given two pay options:

Option A: Base salary of $20,000 a year with a commission of 12% of your sales

Option B: Base salary of $26,000 a year with a commission of 3% of your sales

How much electronics would you need to sell for option A to produce a larger income?

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When hired at a new job selling electronics, you are given two pay options:

Option A: Base salary of $10,000 a year with a commission of 9% of your sales

Option B: Base salary of $20,000 a year with a commission of 4% of your sales

How much electronics would you need to sell for option A to produce a larger income?

Option A:  y = 0.09 x  + 10,000 where x is dollars of sales Option B:  y = 0.04 x + 20 , 000  where x is dollars of sales 0.09 x + 10 , 000 0.04 x + 20 , 000 0.05 x + 10 , 000 20 , 000 0.05 x 10 , 000 x 200 , 000 So, more than $200,000 in sales .
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Source:  OpenStax, Algebra and trigonometry. OpenStax CNX. Nov 14, 2016 Download for free at https://legacy.cnx.org/content/col11758/1.6
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