# Discrete Probability Distributions

• Dec 10th 2012, 10:09 PM
ramil13
Discrete Probability Distributions
Hey, I'm getting ready for my final exam and I don't understand this question.This is a textbook example question(i know the answer to this)

Agway, a farm and garden supply store, sells winter fertilizer in 50-pound bags. For customers purchasing this product, the probability distribution for the random variable X, the number of bags sold, is given in the table that follows.

x 1 2 3 4 5
p(x) 0.55 0.35 0.07 0.02 0.01

d) Suppose two customers are randomly selected. What is the probability that the total number of bags purchased will be at least eight
n = intersect(upside down "U")
Answer : P(x1=4 n x2 = 5) + P(x1= 4 n x2 = 4)
+ P(x1 = 4 n x2 = 5) + P(x1 = 5 n x2 = 3) + P(x1 = 5 n x2 = 4) + P(x1 = 5 n x3 = 5)
= 0.0007 + 0.0004 + 0.0002 + 0.0007 + 0.0002 + 0.0001

My question is I don't understand how every P is calculated and what it means when x1 = one of those numbers and interesects the other number

Also a question about Probability Distribution :

In a paper by Simosohn and Ariely, the authors stued eBay auctions for DVD movies. For a randomly selected patron who places a \$10 bid on a DVD movie with a starting price of \$6, the probability of winning the auction is 0.30. Suppose three patrons who bid \$10 on a DVD movie with starting price \$6 are selected at random. Let the rarndom variable X be the number of patrons who win their auctions.

a) construct the probability distribution for X.

x 0 1 2 3
p(x) 0.343 0.441 0.189 0.027

How is that constructed where is p(0) ... etc found?

Thanks a lot for whoever trys or helps me