Writing Equations

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

Math questions should be read carefully so that you understand each part of the problem.  Take a moment to make a note of the bottom line, the answer you are asked to find, to make sure that you do not accidently solve for the wrong variable or do more work than the problem requires.  Assess your options for solving the problem, choose the most efficient method, and then attack the problem!  Always loop back to make sure that your answer matches the bottom line.

There are n students in a biology class, and only 6 of them are seniors. If 7 juniors are added to the class, how many students in the class will not be seniors?

For this question it is easiest to look at one piece of information at a time.  Your bottom line is the number of students who are not seniors.  Start with the n first.  The n represents the total number of students in the class.  Then you have 6 students from the class that are seniors.  Since you want the number that are not seniors, you must subtract the 6 from the n:
n – 6

Now look at your second piece of information.  7 juniors are added to the class.  Because they are not seniors, they will be added to the number of students who are not seniors:
n – 6 +7

You are not given any more information.  Simplify the equation that you have written:
n + 1

Even though you have not found an exact number, this equation represents the number of students in the class that will not be seniors.  Now look down at your answer choices.

(A) n – 3
(B) n – 2
(C) n – 1
(D) n + 1
(E) n + 2

The correct answer is (D).


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

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