Couple stat. problems.

• Jun 25th 2006, 04:16 PM
Jimmy23
Couple stat. problems.
Hi, I just started a stat. class and I'm not quite sure how to do these two homework problems. Any help would be appreciated...thanks!

Problem 1: A probability distrubtion is partially given in the following table with the additional information that the even values of random variable X are equally likely to occur:

x -------P(X=x)
---------------
1--------0.20
---------------
2-----------?
---------------
3--------0.20
---------------
4-----------?
---------------
5--------0.30
---------------
6-----------?

Find the missing probabilities in the above distribution.

Problem 2: Given below is a summary for the midterm grades of a general physics course.
n=40
sample mean=74
Q1=63
Q2=76
Q3=84

At most, _____ students scored below 63.

I have any exam coming up and I know there will be two problems similar to these, so feel free to be as detailed as possible! Thanks again!
• Jun 26th 2006, 06:06 AM
CaptainBlack
Quote:

Originally Posted by Jimmy23
Hi, I just started a stat. class and I'm not quite sure how to do these two homework problems. Any help would be appreciated...thanks!

Problem 1: A probability distrubtion is partially given in the following table with the additional information that the even values of random variable X are equally likely to occur:

x -------P(X=x)
---------------
1--------0.20
---------------
2-----------?
---------------
3--------0.20
---------------
4-----------?
---------------
5--------0.30
---------------
6-----------?

Find the missing probabilities in the above distribution.

The probability of some outcome (the set of all possible outcomes) must be 1
(that is something must happen). The outcomes: 1, 3, 7 account for a
total probability of 0.7. This leaves a total probability of 0.3 for the three
remaining outcomes which we are told are equally likley so each of them has
a probability of 0.1.

RonL
• Jun 26th 2006, 06:13 AM
CaptainBlack
Quote:

Originally Posted by Jimmy23
Problem 2: Given below is a summary for the midterm grades of a general physics course.
n=40
sample mean=74
Q1=63
Q2=76
Q3=84

At most, _____ students scored below 63.

Q1, Q2 and Q3 denote the quartiles of the course grades. This means that
25% (or 0.25=1/4) of grades were below 63, 50% were below 75 and 75%
were below 84.

So at most 10 students scored below 63.

RonL
• Jun 26th 2006, 11:58 AM
Jimmy23
Thanks alot. I originally thought that the answer was 0.1, but I'm always second guessing myself. Guess I should just trust my answers sometimes. Thanks again!