Blog

SAT Math: Data Analysis

Probability

Screen Shot 2013-12-20 at 1.31.04 PM.jpg

Knowsys Method

Read the question carefully.  Take notice of important information.  You need to determine the probability of rolling two numbers that add up to 8.

Identify the bottom line.  probability that sum will be 8 = ?

Assess your options.  You need an organized way to keep track of all the possible rolls that could add up to 8.  A simple method is to create a table.  

Attack the problem.  Imagine that one of these dice is blue and one is red.  Set up a table with two columns, one for the blue die, and one for the red die. These dice have values 1-6 on their faces, so what sets of numbers between 1 and 6 add up to 8?  There’s 2 and 6, 3 and 5, and 4 and 4.  

Screen Shot 2013-12-20 at 1.31.14 PM.jpg

But you cannot stop there.  You could also have a blue 6 and a red 2 or a blue 5 and a red 3.  Fill in those values now.  

Screen Shot 2013-12-20 at 1.31.22 PM.jpg

To find the probability of rolling one of these combinations, you have to understand probability. 

Screen Shot 2013-12-20 at 1.31.33 PM.jpg

You need to find the probability for each of the combinations you have listed on your chart.  You are trying to figure out the probability of rolling two numbers at the same time, so you need to use probability rule 1.  

Screen Shot 2013-12-20 at 1.31.45 PM.jpg

Now, you need to figure out the probability of rolling any of these 5 combinations, so use probability rule 2 and add the probabilities together.

Screen Shot 2013-12-20 at 1.31.52 PM.jpg

Loop back.  Verify that you solved for the bottom line and select the correct letter.

The correct answer is B.

Want some help reviewing the math concepts you need to master?  Try out the Knowsys Pre-Algebra Flashcards, the Knowsys Algebra I Flashcards, and the Knowsys SAT & ACT Math Practice book.  

Subscribe to Knowsys SAT & ACT Blog by Email