Mathematics > Standard Multiple Choice
Read the following SAT test question and then click on a button to select your answer.
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?
(A) None
(B) One
(C) Seven
(D) Thirteen
(E) More than thirteen
The Correct answer is C.
Explanation
The intersection of sets 
and 
is the set of integers that are in 
and also in 
. Set
consists of all positive integers that are multiples of 
, and set 
consists of all positive integers that are multiples of 
, so the intersection of 
and 
is the set of positive integers that are multiples of both 
and 
. This is the set of all positive integers that are multiples of 
. There are an infinite number of positive integers that are multiples of 
, so there are more than thirteen integers in the intersection of 
and 
.