# Probability problem.

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• May 29th 2010, 10:59 AM
dnntau
Probability problem.
How would I find the answer to...
In a class with 50 students, 25 of the students are female, 15 of the sudents are mathematics majors, and 10 of the mathematics majors are female. If a student in the class is to be selected at random, what is the probability that the student selected will be female or a mathematics major or both?
• May 29th 2010, 11:05 AM
zh305
Pr[X is female or X is maths major or x is female and maths major]
=Pr[X is female or X is maths major]
=Pr[X is female] + Pr[X is maths major] - Pr[X is female and maths major]
=25/50 + 15/50 - 10/50
=30/50
• May 29th 2010, 11:26 AM
dnntau
That worked. (Rofl)
Thanks so much.
• May 29th 2010, 03:03 PM
Soroban
Hello, dnntau!

Quote:

In a class with 50 students, 25 of the students are female,
15 of the students are math majors, and 10 of the math majors are female.

If a student in the class is to be selected at random, what is the probability
that the student selected will be female or a mathematics major or both?

You can draw a Venn diagram or put the data into a chart . . .

. . $\begin{array}{c||c|c||c|}
& \text{Math} & \text{Other} & \text{Total} \\ \hline \hline
\text{Female} & 10 & & 25 \\ \hline
\text{Male} & & & 25 \\ \hline \hline
\text{Total} & 15 & 35 & 50 \end{array}$

Fill in the empty cells and answer the question.