# Probability Models

• Feb 14th 2013, 09:26 PM
arrogantandy
Probability Models
Hello all, I missed a few days in my statistics class, and I need help with some homework, the question is as follows:

Information:

According to the current population survey, the following table summarizes probabilities for randomly selecting a full-time student in various age groups:

Age 15-17 18-24 25-34 35 or older
Probability 0.007 0.573 0.260 0.160

Question: If we randomly select a full time student, what is the probability that he/she is 25 or older?

Second question: If we randomly select a full time student, what is the probability that he/she is NOT 18-24 years old?

I would appreciate solutions, and/or the steps that must be taken to find them.

regards,
-andrew
• Feb 14th 2013, 09:51 PM
MINOANMAN
Re: Probability Models
Arrogantandy.

Selecting a student 25 years old or older means that he/she is either in the classe 25-34 or 35 older...Since these two events are mutually eclusive add the two probabilities to find P(25-34 or older than 35)=0.260+0.160=0.420

if A is the event to select a student between 18-24 then the complement event is not to select a student from the class 18-24 therefore
P(not to select a student 18-24)=1-0.573=0.427
Please study the algebra of events and revise the Ven diagrams that will help you in the study of probabilities.
Good Luck
MINOAS
• Feb 14th 2013, 10:09 PM
arrogantandy
Re: Probability Models
I sincerely appreciate that.

Furthermore, my teacher is very notorious for providing his/her students with a complete lack of resources. Do you know of any good, free online sources that I could utilize in the future?

In continuation, my teacher covered something called a "probability density" the graph of which is attached to this reply as a picture. the teacher wanted us to use that graph to answer these questions:

What is the probability that X is between 0.5 and 1.5 -- what is the probability that x is at least 0.5 -- what is the probability that x = 1.5? why?

Once again, I would appreciate answers, but I would love to know the steps as well.

I know that this math may seem rudimentary to you, but I am at a loss here, and I do appreciate your help.

Regards,
-andrew

Attachment 27021
• Feb 14th 2013, 10:51 PM
MINOANMAN
Re: Probability Models
IF YOU ARE AN IG student scheck in your city to find some good books for statistics and probabilities for beginners.
the math of grade 10 have some chapters have a look on them.

good luck
Minoas