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Ratios And Rates Ratios And Rates Presentation Transcript

  • Ratios and Rates Monday, January 25, 2010
  • Vocabulary
    • Ratio – a comparison of two quantities using division
    • Equivalent ratios – ratios that name the same comparison
    • Rate – compares two quantities that have different units of measure (price per # of liters)
    • Unit rate – when the comparison is to one unit (price per 1 liter)
  • Writing Ratios
    • There are three different ways to write a ratios, and three ways to look at ratios. *Part to part *Part to whole *Whole to part
  • Writing Ratios
    • The table at the right shows the different genres of CDs that make up a student’s CD collection.
    • I want to write a ratio comparing the number of country CDs to the number of rock CDs. *Part to part*
    • So…I could write this three different ways: 8 to 6, 8:6, or 8/6
    2 Salsa 6 Rock 4 Rap 8 Country
  • Writing Equivalent Ratios
    • Let’s say we want to again compare country CDs to Rock CDs, but I want to find two equivalent ratios to the one I write (8:6).
    • I could start of by simplifying (like I did with fractions) 4:3, or I could increase those numbers by a constant (multiply by 2) 16:12
    • 4:3 and 16:12 are equivalent ratios to 8:6
    2 Salsa 6 Rock 4 Rap 8 Country
  • Rates and Unit Rates
    • This is where you’re going to run in to word problems, but luckily, they won’t be that bad!
  • Rates and Unit Rates
    • Here’s a scenario for you: Ms. Brown goes to the grocery store to buy a 2-liter bottle of Wild Cherry Pepsi. When she gets there, she sees that it costs $1.98 for a 2-liter.
    • To write this as a rate, I look at the price per the number of liters: $1.98/2 liters
  • Rates and Unit Rates
    • Many times, Ms. Brown is trying to be frugal, and wants to know how much she is actually spending per liter to determine which is the better deal. (Unit rate!!) So going back to the Wild Cherry Pepsi…
    • $1.98/2-liters…how much does it cost per liter?
  • Rates and Unit Rates
    • In order to figure this out, I’m going to have to divide…(don’t forget “bottoms out”)
    • 1.98 divided by 2 is 0.99, so… The Wild Cherry Pepsi is $0.99 per liter. Not a bad price!