Assignment 4 Questions
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Transcript of Assignment 4 Questions
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Math 4030 SA – Probability and Statistics
Assignment #4
(Due: 4:00 PM, Thursday, May 16, 2013)
1. Prove that for Poisson distribution
( 1; ) ,( ; ) 1
f xf x x
λ λλ
+=
+ for 0,1,2,3,...x =
2. Use the recursion formula in above question 1 to calculate the probability values of a Poisson distribution with 2.5λ = , for 0,1,2,3,4,5,6,7,8,9x = . Draw the probability
histogram of the distribution.
3. Use Table 2 to find
(a) (4;7)F ;
(b) (4;7)f ;
(c) 19
6( ;8)
kf k
=∑ .
4. At a checkout counter customers arrive at an average of 1.5 per minute. Find the probabilities that
(a) Exactly 1 will arrive in any given minute;
(b) Exactly 2 will arrive in any given minute;
(c) At most 5 will arrive in any given minute;
(d) At least 4 will arrive during any interval of 3 minutes;
(e) At most 10 will arrive during any interval of 10 minutes.
5. In a given city, 5% of all drivers get at least one parking ticket per year. Use the Poisson approximation to binomial distribution to determine the probability that among 90 randomly chosen drivers:
(a) 4 will get at least one parking ticket in any given year;
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(b) At least 3 will get at least one parking ticket in any given year;
(c) At most 8 will get at least one parking ticket in any given year.
6. In a “torture test”, a light switch is turned on and off until it fails. If the probability that the switch will fail at any time when it is turned on or off is 0.0015, what is the probability that the switch will survive 1000 turnings of on or off without fail? (Assuming that the conditions for geometric distribution are met.)
7. Random variable X is defined below. For each case, identify the distribution of X (Binomial, Hypergeometric, Poisson, Geometric, or Negative Binomial), as well as the values of the parameters.
(a) Flip a balanced coin 400 times, let X be the number of heads observed.
(b) A class has 12 female students and 42 male students. Randomly select 6 students to form a team. Let X be the number of female students on the team.
(c) A basketball player makes 85% of her free throws. Let X be the number of successful shots she will make before the first miss.
(d) Computer breakdown happens randomly, 1.5 times a week on average. Let X be the number of breakdowns happened in any given day.
(e) A candidate invited for a visit has probability of 0.3 of being hired. Let X be the number of candidates who have been invited for a visit before 2 of them are hired.
8. As can easily be shown, the probabilities of getting 0, 1, 2, or 3 heads from tossing 3 balanced coins are 0.125, 0.375, 0.375, and 0.125. What is the probability of getting 2 heads twice, 1 head 3 times in 6 tosses of these 3 coins?
9. The probability density function of a random variable is given by
2 , 0 2,( )
0, .kx x
f xelsewhere
⎧ < <= ⎨⎩
Find
(a) The constant k ;
(b) (0 1)P x< < ;
(c) (1 6)P x< < ;
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(d) Mean of the random variable X;
(e) Variance of the variable X.
10. If a random variable has the standard normal distribution, find the probability that it will take on a value(s)
(a) Less than 1.25;
(b) Greater than 2.5;
(c) Less than – 1.2;
(d) Greater than – 3.1;
(e) Between 0 and 2.3;
(f) Between 1.22 and 2.43;
(g) Between – 1.45 and – 0.45;
(h) Between – 1.70 and 1.35;
11. Find z if the probability that a standard normal distributed random variable will take on a value is
(a) Less than z is 0.98;
(b) Great than z is 0.21;
(c) Greater than z is 0.5;
(d) Greater than z is 0.65;
(e) Less than z is 0.025.
12. Given a random variable having the normal distribution with 15.2μ = and 2 1.56σ = , find
the probabilities that it will take on a value
(a) Greater than 15.1;
(b) Less than 12.5;
(c) Between 12.0 and 17.5;
(d) Between 16.5 and 16.8.
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13. Find the quartiles of the standard normal distribution 0.25z− , 0.50z , and 0.25z .
14. A stamping machine produces can tops whose diameters are normally distributed with a standard deviation of 0.01 inch. At what “normal” (mean) diameter should the machine be set so that no more than 5% of the can tops produced have diameters exceeding 3 inches?
15. If a random variable has the binomial distribution with n = 40 and p = 0.36, use the normal approximation to determine the probabilities that it will take on
(a) A value greater than 20;
(b) A value less than 15;
(c) The value 15.
Note: in this question np is not large enough to use normal to approximate the binomial, but for practice purpose we will do it anyway.