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Margaret considers five purchases in the amounts 5, 17, 21, 8, 15 dollars with respective probabilities 0.37, 0.22, 0.38, 0.81, 0.63. Anne contemplates sixpurchases in the amounts 8, 15, 12, 18, 15, 12 dollars. with respective probabilities 0.77, 0.52, 0.23, 0.41, 0.83, 0.58. Assume that all eleven possible purchases form anindependent class.

  1. What is the probability Anne spends at least twice as much as Margaret?
  2. What is the probability Anne spends at least $30 more than Margaret?
cx = [5 17 21 8 15 0];pmx = minprob(0.01*[37 22 38 81 63]);cy = [8 15 12 18 15 12 0];pmy = minprob(0.01*[77 52 23 41 83 58]);[X,PX] = canonicf(cx,pmx);[Y,PY] = canonicf(cy,pmy);icalc Enter row matrix of X-values XEnter row matrix of Y-values Y Enter X probabilities PXEnter Y probabilities PY Use array operations on matrices X, Y, PX, PY, t, u, and PM1 = u>= 2*t; PM1 = total(M1.*P)PM1 = 0.3448 M2 = u - t>=30; PM2 = total(M2.*P)PM2 = 0.2431
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James is trying to decide which of two sales opportunities to take.

  • In the first, he makes three independent calls. Payoffs are $310, $380, and $350, with respective probabilities of 0.35, 0.41, and 0.57.
  • In the second, he makes eight independent calls, with probability of success on each call p = 0 . 57 . He realizes $100 profit on each successful sale.

Let X be the net profit on the first alternative and Y be the net gain on the second. Assume the pair { X , Y } is independent.

  • Which alternative offers the maximum possible gain?
  • What is the probability the second exceeds the first— i.e., what is P ( Y > X ) ?
  • Compare probabilities in the two schemes that total sales are at least $600, $700, $750.
cx = [310 380 350 0];pmx = minprob(0.01*[35 41 57]);Y = 100*[0:8];PY = ibinom(8,0.57,0:8); canonicEnter row vector of coefficients cx Enter row vector of minterm probabilities pmxUse row matrices X and PX for calculations Call for XDBN to view the distributionicalc Enter row matrix of X-values XEnter row matrix of Y-values Y Enter X probabilities PXEnter Y probabilities PY Use array operations on matrices X, Y, PX, PY, t, u, and Pxmax = max(X) xmax = 1040ymax = max(Y) ymax = 800PYgX = total((u>t).*P) PYgX = 0.5081k = [600 700 750];px = zeros(1,3); py = zeros(1,3);for i = 1:3 px(i) = (X>=k(i))*PX'; endfor i = 1:3 py(i) = (Y>=k(i))*PY'; enddisp([px;py]')0.4131 0.2560 0.2337 0.07840.0818 0.0111
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A residential College plans to raise money by selling “chances” on a board. There are two games:

  • Pay $5 to play; win $20 with probability p 1 = 0 . 05 (one in twenty)
  • Pay $10 to play; win $30 with probability p 2 = 0 . 2 (one in five)

Thirty chances are sold on Game 1 and fifty chances are sold on Game 2. If X and Y are the profits on the respective games, then

X = 30 · 5 - 20 N 1 and Y = 50 · 10 - 30 N 2

where N 1 , N 2 are the numbers of winners on the respective games. It is reasonable to suppose N 1 binomial ( 30 , 0 . 05 ) and N 2 binomial ( 50 , 0 . 2 ) . It is reasonable to suppose the pair { N 1 , N 2 } is independent, so that { X , Y } is independent. Determine the marginal distributions for X and Y then use icalc to obtain the joint distribution and the calculating matrices. The total profit for the College is Z = X + Y . What is the probability the College will lose money? What is the probability the profit will be $400 or more, less than $200, between $200 and $450?

N1 = 0:30; PN1 = ibinom(30,0.05,0:30);x = 150 - 20*N1; [X,PX]= csort(x,PN1); N2 = 0:50;PN2 = ibinom(50,0.2,0:50); y = 500 - 30*N2;[Y,PY] = csort(y,PN2);icalc Enter row matrix of X-values XEnter row matrix of Y-values Y Enter X probabilities PXEnter Y probabilities PY Use array operations on matrices X, Y, PX, PY, t, u, and PG = t + u; Mlose = G<0; Mm400 = G>= 400; Ml200 = G<200; M200_450 = (G>=200)&(G<=450); Plose = total(Mlose.*P)Plose = 3.5249e-04 Pm400 = total(Mm400.*P)Pm400 = 0.1957 Pl200 = total(Ml200.*P)Pl200 = 0.0828P200_450 = total(M200_450.*P) P200_450 = 0.8636
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Source:  OpenStax, Applied probability. OpenStax CNX. Aug 31, 2009 Download for free at http://cnx.org/content/col10708/1.6
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