8.2.1 Two and Three Term Ratios

One of the simplest recipes is for making Rice Krispie Treats.  This has only 3 ingredients:

  • 3 tablespoons of butter/margarine
  • 40 marshmallows
  • 6 cups of Rice Krispies

What if you only had 10 marshmallows?  How much of each ingredient should you use?  This is what ratios are good for, for thinking proportionally.  Today, we'll look at ratios in more detail.


Videos or watch the Playlist for all 4 videos


  • p51 #5-8, 10-13, 15, 17, 20 *21

Things you should know how to do after today:

Read more: 8.2.1 Two and Three Term Ratios

8.2.2 Unit Rates

Recall that ratios are comparisons between two things.  For example, you could make a ratio comparing the number of boys to girls because those are both things that you count.  You could make a ratio of time spent on math and time spent on english, because those are comparisons of time.

When we make a comparison between things that are counted in different ways, then that is called a rate instead of a ratio.  Find out about rate, unit rate and unit pricing to find out what they are useful for.

You will need to watch the videos for lesson 2.  You can watch the whole playlist at once, or each of the videos separately:


  • p60 #4, 5, 7, 8, 10, 12, 14, 15
  • Bulk Mayonnaise Assignment (8L is a lot, but maybe Dan owns a restaurant...ever think of that?)

Things you should know after today:

  • How is a rate different from a ratio?
  • How can unit price be used to determine a better buy
  • How can you calculate a unit rate
  • How can unit price and unit rate be used to solve a problem
FileDescriptionFile size
Download this file (2.02 Mayonnaise.pdf)2.02 Mayonnaise.pdf 53 kB

8.2.3 Proportional Reasoning

Many problems are solved using ratios, but there are many ways to find the solution to a ratio problem.   Two of the methods include:

  • using a unit rate
  • using a proportion

A proportion is simply when an equivalent ratio is setup (using either a fraction or ratio notation) and then an equivalent ratio is made.  There are a couple of different ways to find the missing value in your equivalent ratio.

Watch the 4 videos on proportional reasoning:

  1. Introduction to proportions
  2. Solving a problem using either proportions or unit rate
  3. How the capture-release-recapture method of estimating natural populations is actually proportional reasoning
  4. Example using pricing/unit pricing.

4 video playlist


Things you should know how to do after today:

  • use proportions or unit rates to solve proportional situations (involving ratios)

8.2.4 Review


  • p70 #1-5, 6, 8, 9, 11, 12, 14,-17
  • Finish the Projected Sales part of the unit project
  • Did you hand in your Mayonnaise Assignment?

Study Guide

Terms to know:

  • Two term ratio
  • three term ratio
  • part to part ratio / part to whole ratio : What is the difference between them? 
  • rate / unit rate : What is the difference between a rate and a unit rate?
  • unit price
  • proportion

Things to know how to do:

  • How to write ratios in lowest terms
  • How to make equivalent ratios
  • When can a ratio be converted into a percent or a decimal?
  • How do you compare prices to find best buys?
  • How do you convert a ratios to decimals and/or percents
  • How to use proportions to find equivalent ratios
  • Use proportions to solve proportional situations involving ratios


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