Investing Exponential Functions

Tyrell decides to invest $20 in stock at Target. The stock increases 1.8% each year.

Write an equation to model the situation then find how much money this stock will be worth in 6 years.

• y = 20 (1.018)^x

  
  

  $22.26

• y = 20 (0.018)^x

  
  

  $1.11

• y = 20 (0.982)^x

  
  

  $17.93

• y = 1.8 (20)^x

  
  

  $115,200,000

After it has been harvested, corn stored at a particular temperature will lose market value at a rate of 10% per day. If a corn harvest worth $68,000, write the exponential equation and find how much it is worth in 2 days.

• y = 68000 ( 10)^x

  $6,800,000

• y = 2 (10 )^x

  $200

• y = 68,000 (0.9)^x

  $55,080

• y = 68000 (1.1)^x

  $82, 280

The compact disc format has been declining in popularity, and one music executive has predicted that CD sales will decrease by 20% per year. If the executive's company started selling 3,900,000 CDs this year, how many will the company sell 4 years from now?

• y = 3, 900, 000 (0.8)^x

  $12,480, 000

• y = 3, 900, 000 (0.8)^x

  $1,597,440

• y = 3,900,000 (4)^x

  $1,597, 440

• y = 20 (4)^x

  $12, 480, 000

A town doubles its size every 5 years. If the population is currently 500, write an equation and find what will the population be in 20 years?

• y = 500 (.2)^x

  0.8 people

• y =5 (2)^x

  80 people

• y = 500 (2)^x

  524, 288, 000 people

• y = 500 (2)^x

  8,000 people

Rachel has $30 in a savings account that earns 10% interest, compounded annually.

Write an equation and find To the nearest cent, how much will she have in 3 years?

• y = 30 (1.1)^x

  $39. 93

• y = 30 (0.1)^x

  $0.03

• y = 30 (10)^x

  $399.30

• y = (1.1)^x

  $45.67

There is a population of 10,000 bacteria in a colony. If the number of bacteria doubles every half hour, what will the population be 3 hours from now?

• y = 10,000 ( 2 ) ^x

  80, 000 bacteria

• y = 10,000 ( 2 ) ^x

  640, 000 bacteria

• y = 3 ( 2 ) ^x

  24 bacteria

• y = 10,000 ( .2 ) ^x

  80 bacteria

Identify the initial value:

y = 6.87 (4)^x

• a = 4

• a = 6.87

• a = 3

• a = 1

Does the following equation represent exponential growth or decay? Explain.

y = 5 ( 0.3) ^x

• Decay because 0 < 0.3 < 1

• Decay because 0.3 < 1

• Growth because 5 >1

• Neither