Of the 100 students at a certain school, 30 students are taking

Question

Of the 100 students at a certain school, 30 students are taking a chemistry class, 40 students are taking a physics class, and 20 students are taking both a physics and a chemistry class. If a student is chosen at random from the school, what is the probability that he or she is taking a physics or a chemistry class?

A. 1/4
B. 3/10
C. 5/12
D. 1/2
E. 3/5

A. 1/4
B. 3/10
C. 5/12
D. 1/2
E. 3/5

divyadna · Answer

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gmatophobia · Answer

We can use a 2*2 matrix to analyze the data.

P(Physics or Chemistry) = 1 - P(None)

None = 50 students

P(Physics or Chemistry) =  1 - \frac{50}{100} = \frac{1}{2}

Rohit_842 · Answer

When the question is mentioning "physics OR a chemistry class" why aren't we considering only physics and only chemistry. Why should I include students with both chemistry and physics. Please help.

Krunaal · Answer

The question does not ask  only  physics or  only  chemistry or  only one of the two , the idea here is to understand that out of the 100 students  there are students who are taking neither the physics class nor the chemistry class.

Now, when we remove those students from the 100, each student is taking either physics or chemistry or both. Think, if you select someone taking both, and I simply ask is he/she taking a physics or chemistry class and you have to answer only in yes or no, what would your answer be?

Of the 100 students at a certain school, 30 students are taking

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Of the 100 students at a certain school, 30 students are taking

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