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Unformatted text preview: Probability and Statistics for Engineering (ESE 326) Final Exam May 9, 2011 This exam contains 19 multiple—choice problems worth two points each and 12 truefalse problems
worth one point each, for an exam total of 50 points. Part I. MultipleChoice (two points each) Clearly ﬁll in the oval on your answer card which corresponds to the onlyr correct response. 1. What is the probability that a ﬁve—card hand selected randomly from a standard 52card deck will
be a “threeof—a~kind”? (Such a hand consists of three cards of the same kind together with two cards whose kinds do not match the ﬁrst three or each other. An example is 9 0 310,91! ,Av,5 0 .) (A) .0070
(B) .0123
(C) .0211
(D) .0226
(E) .0423
(F) .0451
(G) .0595
(H) .0616
(I) .0824
(J) .0872 2. Suppose A and B are events such that P[AIB] = .7, P[A’ m B’] 2 .16, and P[B] 2 .6. Find
PM].
(A) .24
(B) .40
(C) .42
(D) .504
(E) .588
(F) .6864
(G) .66
(H) .7143
(I) .8333
(J) .8571 3. Consider the discrete random variable X Whose density is given by the following table. Find
ElX]. (A) g = 1.5 (B) 3 = 1.6 (C) : = 1.75
(D) g : 1.8 (E) 2 (F) 13: m 2.2 @
ll
NJ
to
O1 @
W MlCﬂ 045 (JrIce m
5
to
,4; (I) m 2.5 A
3 4. Gambler Gus has a weighted coin which comes up heads Only 40% of the time. He places a bet
with Saloon Sally that if he flips his coin 10 times, more than half of the ﬂips will come up tails.
What is the probability that Gambler Gus will lose his bet? (A) .1662
(B) .3669
(o) .3823
(D) .4512
(E) .5 (F) .5488
(G) .6177
(H) .6331
(I) .8338 There are 101 students in a physics class, speciﬁcally, 22 sophomores, 50 juniors, and 29 seniors.
If the instructor randomly selects three students to be on a speciai Advisory Panel, what is the probability that at least two are juniors? (A) .1176
(B) .2426
(C) .2723
(D) .3749
(E) .4926
(F) .5075
(G) .6251
(H) .7277
(I) .7574
(J) .8824 The arrival of patients at the Emergency Room of a smalltown hospital is a Poisson process, where
A 2 20 patients per day. What is the probability that the ﬁrst patient of the day arrives during the
second hour (1:00 am. to 2:00 am)? (Of course, the ER is open 24 hours a day, and each day
begins at midnight.) (A) .1509 (B) .1574 (C) .1889 (D) .2457 (E) .3344 (F) .3622 (G) .4346 (H) .5654 (I) .6656 (J) .7543 7. Consider the continuous random variable X with the density function shown below. Find the
median of X. f(93) I 82:”, a: > 2 (A) 2 (B) 2x/5
(C) 2 3
(D) 4 (E) 4V5
(I) 4\/§ (G) 8
(H) 8V5
(I) 8\/§ 8. Consider the continuous random variable X with the density function shown below. Find the
variance of X. f(;c)=2—2x,0ga:51
(A) ~1—
(B) 3—
(C) ~1—
(D) i
(E) i
(F)
(G) (I) .1,
9
J;
8
(H) l;
l
4
(J) g 9. 10. Consider the two»dimensional random variable (X, Y) with the joint density shown below. Set up
the integral which would be needed to find P[Y > X]. You do not need to work out the integration. fxy(x,y)2§my,1s:cs3,osys2 on jfjfgxydydm (B) ffffgmydyda
(C) jfjfgmydydx (D) jfjfgxydydx
(E) jfj:%xydydx no jfjfgxydydx
an jfjjéxydydx on jfjfgxydydm Consider the following theorem and proof. Which step in the proof uses the assumption that
X1, . .. ,Xn is a random sample? (Note that a “step” is a transition from one line to the next. For
example, (A) is the correct choice if the transition from the ﬁrst line to the second line in the proof uses the random sample assumption.) Theorem. Let X be a random variable with mean n, let X1, . . . , X“ be a random sample of size n from the distribution of X, and let X = ZXg  111 be the sample mean. Then E[X] = [in
1'21 Proof. E[Y]
n it (A)
=E{Z& Q
121
ﬂ it (B)
2% an]
n l} (C)
: lE [ 2X1]
i=1
n ll (D)
ixl
n ii (E)
=tzmn
i=1
n ii (F)
Zia“
it (G)
==%(nn)
ll (H) ll. Suppose a random variable X has mean ,u : 80 and variance 0‘2 z 25. Let X1, ,X4 be a random sample of size n = 4 from the distribution of X. According to Chebyshev’s Inequality, at least 3 of the sample means in the distribution of X will lie in what interval? (A) 77.5 < 3?" < 82.5
(B) 75 < 1)? < 85 (C) 73.75 < 32'" < 85.25
(D) 72.5 < “X” < 87.5
(E) 70 < 3? < 90 (F) 57.5 < “X” < 92.5
(G) 65 < X < 95 (H) 51.25 < ”X“ < 98.75
(I) 55 < ”X" < 105 (J) 30 < f < 130 12. Suppose X is a normal random variable with unknown mean ,LL and unknown standard deviation 0.
The statistic s : .8 is obtained from a random sample of size n m 10. Find the left endpoint L1 for
a 92% conﬁdence interval for the standard deviation 0. (A) .33
(B) .41
(C) .57
(D) .55
(E) .54
(F) 1.35
(G) 1.44
(H) 1.52
(I) 1.85
(I) 2.32 13. Suppose a twotailed hypothesis test has null and alternative hypotheses as shown.
H0: [1. z 7 H1: ii 75 7 A random sample yields the sample mean 233" 2 10. Which of the following is the correct setup for
computing the P value? (A) P[M%77:10l (B) 2P1M37IX7£101
(C) 2P[,u27l77£10] (D) 2P[ag7f=1o]
(E) 2Piu271fn10] (F) Plfﬂomzﬂ
(G) 2Pl35510Imé7] (H) 2131?: 10mm
(I) 2P[”X':10Iu:7} (I) mfziolurﬂ 14. Let X be a normal random variable, and consider a hypothesis test on the mean ,u, of X having the
following characteristics. it 2 9 0: I .05
H92n=15 H1:,u<15
E = 13 s = 2.8 Find the probability of committing a Type II error given that ,u 2 12. (A) .1003 (B) .1048 (C) .1063 (D) .1260 (E) .1475 (F) .1624 (G) .1641 (H) .1871 (I) .1951 (I) .2267 15. 16. 17. Suppose the signiﬁcance level for a hypothesis test is a = .05, and suppose the P value is .08.
Which of the following statements is correct? (A) We are 95% conﬁdent that Hg is true. (B) We are 95% conﬁdent that H0 is false. (C) We are 95% conﬁdent that H0 is signiﬁcant.
(D) The probability that H; is true is .92. (E) The probability that H0 is false is .92. (F) The probability that H0 is signiﬁcant is .92. (G) None of these statements is correct. Rose is interested in the proportion of American households which do not have a landline. She
takes a random sample of 75 homes and ﬁnds that 21 of them do not have a landline. She uses this
data to construct a confidence interval, which she then decides is unacceptably wide. If Rose starts
her study over, what sample size should she choose in order to obtain a 97% conﬁdence interval with radius at most .04? (A) 445
(B) 445
(C) 598
(D) 594
(E) 735
(F) 736
(G) 944
(H) 945
(I) 982
(J) 988 Consider the following random sample of points. Use the regression line for this data to estimate
y(12).
(5, 24) (10, 28) (15, 55) (20, 62) (25, 88) (A) 35.84 (8) 37.82
(C) 38.80 (D) 49.24
(E) 41.58 (F) 43.25
(G) 44.83 (H) 45.40 (I) 47.97 (1) 49.55 18. 19. A 2—sigma :3? control chart has been set up to monitor the sample means of a normal random
variable X , using samples of size n = 9. When the process is in control, the mean and standard
deviation of X are #0 2 40 and or = 6. The control limits can then be computed to be as follows. _ W i: 3 1L:
LCL—4O 2V5 36 UCL 40+2\/§ 44 Find the average run length (to the nearest integer) if the mean shifts to a = 41.25. (A) 2
(B) 3 (C) 5 (D) 11
(E) 12
(F) 24
(G) 231
(H) 243
(I) 336
(J) 462 In the movie “Case Study” from the video series Against All Odds: Inside Statistics, an account is
given of the clinical trials in which a new medication was tested. What was this medication? (A) Allegra
(B) Amoxcil
(C) AZT (D) Claritin
(E) Lipitor
(F) Prevacid
(G) Ritalin
(H) Vicodin
(I) Zithromax
(J) Zyrtec Part II. TrueFalse (one point each) Mark “A” on your answer card if the statement is true; mark “B” if it is false. 20. For any events A and B, P[BA] : 1 — P[AB]. 21. If the two—dimensional random variable (X, Y) has joint density given by the table below, then X
and Y are independent. 22. Suppose (X , Y) is a twodimensional random variable such that the correlation between X and Y
is PXY 2 —1. Then X and Y are exactly linearly related. 23. Let (X, Y) be a twodimensional random variable, and consider iii/Mm), the curve of regression of
Y on X. For each :13, am gives the mean of Y for that value of m. 24. If X and Y are independent normal random variables, then 0x+y : ox + 01/. 25. Let X be a random variable, and let X1, . .. ,Xn be a random sample of size n from the distribution
of X. If n is large, then, by the Central Limit Theorem, the distribution of X is approximately normal. 26. Suppose a conﬁdence interval for some parameter is being constructed. All other things being
equal, increased reliablility leads to a longer conﬁdence interval. 27. f9 2 if is an unbiased point estimator for p. Consider the usuai situation Where there appears to be a linear relationship between a variable X and a
random variable Y, and where a random sample of points (331,y1), m , (33m yn) has been obtained for the
purpose of ﬁnding a line of regression. Recall that for each i, Y; 2 ﬁg + 6135 + Ei, where E; is an
“error” random variable. Assume that the usual four assumptions on the 131 are satisﬁed. One of those
assumptions is that the ET all have the same variance, which we denote by 02, and it follows that the variance of each Y; is also 02. Use the above information for problems 28 through 30. 28. Si, is an unbiased point estimator for 02. 29. For any as, the conﬁdence intervals for ny‘x and Yzc have the same center. 30. For any 3:, the confidence interval for ”Yin: is shorter than the conﬁdence interval for Yac. 31. For a control chart to give good results, the sample size should be large (n 2 20). ...
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