Question

In the elevator riding up to the 7th floor, five of the students are taking Calculus, seven are taking Discrete Math, three are taking both, and four are taking World History. How many students in the elevator are taking a math class?

Answer 1

In this question, let C denote the set of students who are taking calculus, thus, n(C) denotes the total number of such students.

Here, n(C)= 5

let D denote the number of students taking discrete maths , thus, n(D) denotes the total number of such students.

Here, n(D)=7

Also, students who take both calculus and discrete maths are in the set   , thus, number of such students is

We will completely ignore the world history set as it does not add anything to the question except confusion.

We need to find the number of students who are taking a math class, thus, no role of wolrd history here.So, we have to find

We know that

Thus,

Hence , we get that a total of 9 students are taking a math class.

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