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# Probability homework question ??

Wed 2 May, 2012 01:55 pm
Can someone help me out on this problem>>>???

An advanced course in psychobiology is composed of 30 chemistry majors, 50 biology majors, 45 psychology majors, 50 engineering majors and 25 linguistics majors. All together, the class has 125 women and 75 men.

a. If a single student is drawn randomly from the class, what is the probability that:
1. The student would be a woman?

2. The student would not be a psychology major?

3. The student would be either a biology major or engineering major?

4. The student would be an education major?
b. If two students are drawn randomly from the class, what is the probability that:
1. Both of them would be men?

2. One would be a linguistics major and one would be an biology major?

3. One would be a male chemistry major and one would be a female biology major?

c. If three students are drawn randomly from the class, what is the probability that:
1. At least one would be a linguistic major?

2. The first one draw would yield a psychology major, the second draw a chemistry major and third draw an engineering major.
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1
Wed 2 May, 2012 01:57 pm
@mihanni21 ,
Which question are you having trouble with?
mihanni21

1
Wed 2 May, 2012 02:10 pm
Its ONE question with several parts to it. I don't understand how to work out probability questions???

1
Wed 2 May, 2012 02:17 pm
@mihanni21 ,
Is this part of a class, or a job interview, or what?

Let's start at the top.

125 women. 75 men.

Randomly choose one.

What's the chance that it will be a woman?
mihanni21

1
Wed 2 May, 2012 02:34 pm
This is a homework problem for my online statistics class.

1
Wed 2 May, 2012 02:36 pm
@mihanni21 ,
Are you saying they assigned the work without covering the topic in the class?
mihanni21

1
Wed 2 May, 2012 02:41 pm
There is no actual class, its ALL online. I read the chapter over probability but I'm still somewhat confused on how to work this problem.
0 Replies

markr

1
Wed 2 May, 2012 07:59 pm
@mihanni21 ,
The probability of a particular outcome is the number of ways that outcome can occur divided by the total number of possible outcomes. For instance, if there are 3 men and 7 women, the probability that a woman would be chosen is 7/10 (assuming one person is chosen). There are 7 ways to choose a woman. There are 10 ways to choose a person.

The probability that two women would be chosen is 7/10 * 6/9 (assuming two people are chosen). The 7/10 is for the first woman. After that, 6 of the 9 remaining people are women, so that's where the 6/9 comes from.
mihanni21

1
Wed 2 May, 2012 09:15 pm
@markr,
So for the first part of the question on a1. it would be 125/200 ?? Am I going in the right direction??

and a2. would be 45/200 ??
markr

1
Wed 2 May, 2012 09:31 pm
@mihanni21 ,
Yes and no. You gave the probability that it IS a psychology major. They want the probability that it ISN'T a psychology major.
mihanni21

1
Wed 2 May, 2012 09:41 pm
@markr,
Sooo confusing! How do I go about do that??
markr

1
Wed 2 May, 2012 09:44 pm
@mihanni21 ,
Also:
P(x or y) is P(x) + P(y) if x and y are mutually exclusive (x and y can't both occur simultaneously)
P(x and y) is P(x) * P(y) if x and y are independent
P(x and y) is P(x) * P(y|x) if x and y are dependent

P(y|x) is read "the probability of y occurring given that x has occurred"
0 Replies

markr

1
Wed 2 May, 2012 09:45 pm
@mihanni21 ,
Actually, it's easy. How many students are NOT psychology majors?
mihanni21

1
Thu 3 May, 2012 09:46 am
@markr,
155 are NOT??

1
Thu 3 May, 2012 09:50 am
@mihanni21 ,
Correct. So what is the chance that a randomly chosen student is NOT a psychology major?
mihanni21

1
Thu 3 May, 2012 11:31 am
so 145/200 are NOT psychology majors??

1
Thu 3 May, 2012 11:36 am
@mihanni21 ,
Close. check the number that you had just before this.
mihanni21

1
Thu 3 May, 2012 11:43 am
155/200??

1
Thu 3 May, 2012 11:52 am
@mihanni21 ,
Yes.
mihanni21

1
Thu 3 May, 2012 11:59 am
ok...here is what I came up with for the rest....

1. The student would be a woman? 125/200=5/8

2. The student would not be a psychology major?155/200=31/40

3. The student would be either a biology major or engineering major? 100/200=1/2

4. The student would be an education major?25/200=1/1/4
b. If two students are drawn randomly from the class, what is the probability that:
1. Both of them would be men? 2/75

2. One would be a linguistics major and one would be an biology major?25/200=1/8 would be a linguistics major and 50/200=1/4 would be a biology major

BUT...I can't figure out how to work out b3, OR c 1 and 2????

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