Sets

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Mathematics: Standard Multiple Choice

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

Always follow the Knowsys Method to save time and energy on math questions: read carefully, identify the bottom line, assess your options, attack the problem, and loop back to double-check your answer. This will help you find the correct answers more quickly.

If S is the set of positive integers that are multiples of 7, and if T is the set of positive integers that are multiples of 13, how many integers are in the intersection of S and T?

First, read carefully. Notice that S includes all multiples of 7 and T includes all multiples of 13. Next, identify the bottom line and note it at the top of your scratch work.

Intersection of S and T = ?



You are looking for the intersection, so you need only the numbers that are in both set S and set T. Since neither set has an upper limit, they both have an infinite number of members; therefore, their intersection also has an infinite number of members. Look at the answer choices.

A) None

B) One

C) Seven

D) Thirteen

E) More than thirteen

The answer is E.