Activity 7: Two Friends' Methods

October 24, 2007 through October 31, 2007

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ACTIVITY OVERVIEW

In this activity we will:

  • Investigate decrease in items as a percent change
  • Consider several methods for calculating percent change
  • Develop a procedure that can be repeated to solve problems


  

Milo tells Otis his brother has just purchased a car. “It is worth $20,000."  Every year, “it loses 5% of its value.”  Otis says, “When will it be worth $10,000? Will it take 10 years?”  Milo states, “I have a way to figure this out.  Let me explain it to you.”


  
Start with your $20,000.  Use your calculator.  You can’t do this with your fingers and maybe not in your head.  You’ll see why Otis. Type in the 20,000. Press  to enter that value in your calculator.  When it shows up on the right, the calculator knows your number. no alt text supplied
Press  to multiply and enter .05.  Press .  Then subtract those two numbers.  You can arrow up to each number and press to “grab” the number to use it.  That’s how much is left after 1 year. 
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Write it down in a table with the amount of years in the first column and the new value in the second column.  You’ll find the answer that way. Don’t forget to round the answer to You can do two decimal places. Write this in your notebook or a piece of paper.


  

Otis thinks for a minute.  “I think I have a better way Milo. It will even keep track of the amount of years.”  Milo frowns. “You can’t do that with a calculator.  If you’re so sure, show me how it’s done.”

 
  
Otis press the key and  .  He then sets the calculator to remove 5% of the price constantly. His calculator screen looks just like the one on the right. no alt text supplied
Otis then presses   and then clears the screen by pressing .  He enters the 20,000 and presses .  Then, for each year, he presses .
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You can copy then for the year and the amount next to it that remains.  Again, round it to two decimal places.


 

Compare the two methods and decide which one you like better.   Can you come up with your own method to improve on Milo and Otis’ procedures?


  

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