Scatterplots

Data Analysis: Scatterplots

Read the following SAT test question and then select the correct answer. 

Always read the question carefully so that you can glean as much information from it as possible.  Identify the bottom line – what is it asking?  Then assess your options and choose the most efficient method to attack the problem.  When you have a solution, loop back to make sure that it matches your bottom line.

The scatterplot above shows the number of items purchased at a grocery store by 28 customers and the total cost of each purchase. How many of these 28 customers bought more than 10 items and spent less than $20?

Bottom Line: # of people.  Notice that this number must reflect those that meet 2 requirements: buying more than 10 things and spending less than $20.

Assess your Options:  When you have a graph, use the graph!  You can draw directly on it to help you visualize what you need.

Attack the Problem:  The dots represent each person.  Start with the first restriction.  If people must buy more than 10 items, then only the dots to the right of the 10 on the horizontal axis will be counted; those on the line do not count because they are equal to 10 rather than more than 10.  Draw a vertical line on the 10.  Now look at the second restriction.  If the people must spend less than $20, then they must be under the $20 hash mark on the vertical axis.  Draw a line at $20.  Your graph should look like this:

Count the number of dots in the lower right hand region that you created.  Your answer is 4.

Loop Back:  Each dot represents a customer, a person, so you reached your bottom line.  Look down at your answer choices.

(A) Four

(B) Five

(C) Six

(D) Seven

(E) Eight

The correct answer is (A).

On sat.collegeboard.org, 66% of the responses were correct.

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