Ratio and Probability

Ratio and Probability

In our Ratio and Probability unit we will learn about the chance of an event happening.

 Ratios are one way to compare 2 amounts.  Ratios can be written in three forms: as words, as numbers with a colon separating the two amounts, and as fractions.  For example:  if a class has 14 boys and 15 girls, the ratio of boys to girls is 14 to 15, 14:15, or 14/15.

 The order of the numbers in the ratio is very important.  For example, a class has 14 boys and 15 girls.   If we are comparing girls to boys, the ratio is 15 to 14.  If we are comparing boys to girls, the ratio is 14 to 15.

 Probability is the chance of something happening.  Probability describes whether an event is likely to happen, unlikely to happen, certain to happen, impossible, or more likely, equally likely, or less likely to happen than another event.

 A result of an experiment is called an outcome or event.  Possible outcomes are all the possible results or events that might happen.

 Probability of drawing a card:  There are 52 cards in a deck so what are the chances of picking a King? 

        There are 4 Kings in a deck of cards so the probability of drawing a King would be 4 out of 52.

  Probability of flipping a coin and getting Heads or Tails:  There are 2 sides to a coin so what is the chance of getting a heads or tails if you flip the a coin?

       There is a 1 in 2 chance of getting a head or tail.  Remember every time you flip the coin it is always a 1 in 2 chance of getting a head or tail no matter how many times you flip.

 Probability of rolling dice:  If you roll 1 di what is the chance of rolling a 2? 

       There are 6 sides to a di so and only 1 side of the di has a two.  The chance of rolling a 2 is 1 in 6.

 What if you have 2 dice?  What would be the chance of rolling the dice and having the dice equal 5?  Remember you can get five with 4 + 1 and 2 + 3.

       Making a chart like the one above is very helpful in this type of problem.  There are 36 possible outcomes.  4 of the outcomes will equal 5 so you have a 4 in 36 chance.

 Probability of picking an item:  See the examples below --

 Probabilty of landing on a color on a spinner: What is the probability of landing on yellow when you spin the spinner?

       There is 1 yellow space on the spinner.  There are 4 equal spaces on the spinner.  The chance on landing on yellow is 1 in 4.

 You can also use probability to determine if a game is fair or unfair.  The teacher gives 1 student spinner A and she gives another student spinner B.  She then explains that to win a game the person who spins yellow the most will win.  Is this game fair or unfair?

A    B

       This game is unfair.  The student with spinner A has less of a chance to spin yellow than the student with spinner B.  Spinner A has a 1 in 4 chance.  Spinner B has a 1 in 3 chance.

 To practice probability of rolling dice. 

 To practice probability of choosing a color.

 To practice probability of tossing a coin.  

 To practice probability using cards.

 To practice probability using spinners.  

 To complete a probability tutorial.

 To practice probability of choosing a color.  

 To practice probability using spinners.

 Below is a Probability Power Point that covers what we learned in class.  Click on Probability Power Point and review what we learned in class.

Probability Presentation (ppt file)

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