m16836 Probability Topics: Homework 1.11 2008/05/29 12:00:16 GMT-5 2009/04/29 17:14:30.024 GMT-5 Susan Dean Susan Dean deansusan@deanza.edu Barbara Illowsky Barbara Illowsky, Ph.D. illowskybarbara@deanza.edu Susan Dean Susan Dean deansusan@deanza.edu Barbara Illowsky Barbara Illowsky, Ph.D. illowskybarbara@deanza.edu Connexions Connexions cnx@cnx.org Maxfield Foundation Maxfield Foundation cnx@cnx.org conditional elementary event exclusive independent mutually probability statistics Mathematics and Statistics This module provides a number of homework exercises related to Probability. en Download handout (.pdf) Download handout (.doc) Suppose that you have 8 cards. 5 are green and 3 are yellow. The 5 green cards are numbered 1, 2, 3, 4, and 5. The 3 yellow cards are numbered 1, 2, and 3. The cards are well shuffled. You randomly draw one card. G = card drawn is green E = card drawn is even-numbered aList the sample space. bP(G) = cP(G|E) = dP(G AND E) = eP(G OR E) = fAre G and E mutually exclusive? Justify your answer numerically. a{G1, G2, G3, G4, G5, Y1, Y2, Y3} b 5 8 c 2 3 d 2 8 size 12{ { { size 8{2} } over { size 8{8} } } } {} e 6 8 size 12{ { { size 8{6} } over { size 8{8} } } } {} fNo Refer to the previous problem. Suppose that this time you randomly draw two cards, one at a time, and with replacement. G 1 = first card is green G 2 = second card is green aDraw a tree diagram of the situation. b P ( G 1  AND  G 2 ) = size 12{P \( G rSub { size 8{1} } " and "G rSub { size 8{2} } \) ={}} {} c P ( at least one green ) = size 12{P \( "at least one green" \) ={}} {} d P ( G 2 ∣ G 1 ) = size 12{P \( G rSub { size 8{2} } \lline G rSub { size 8{1} } \) ={}} {} eAre G 2 size 12{G rSub { size 8{2} } } {} and G 1 size 12{G rSub { size 8{1} } } {} independent events? Explain why or why not. Refer to the previous problems. Suppose that this time you randomly draw two cards, one at a time, and without replacement. G1 = first card is green G2 = second card is greenaDraw a tree diagram of the situation. b>P( G1  AND  G2 ) = cP(at least one green) = dP( G2 | G1 ) = eAre G2 and G1 independent events? Explain why or why not. b ( 5 8 ) ( 4 7 ) size 12{ \( { { size 8{5} } over { size 8{8} } } \) \( { { size 8{4} } over { size 8{7} } } \) } {} c ( 5 8 ) ( 3 7 ) + ( 3 8 ) ( 5 7 ) + ( 5 8 ) ( 4 7 ) size 12{ \( { { size 8{5} } over { size 8{8} } } \) \( { { size 8{3} } over { size 8{7} } } \) + \( { { size 8{3} } over { size 8{8} } } \) \( { { size 8{5} } over { size 8{7} } } \) + \( { { size 8{5} } over { size 8{8} } } \) \( { { size 8{4} } over { size 8{7} } } \) } {} d 4 7 size 12{ { { size 8{4} } over { size 8{7} } } } {} eNo Roll two fair dice. Each die has 6 faces. aList the sample space. bLet A be the event that either a 3 or 4 is rolled first, followed by an even number. Find P(A). cLet B be the event that the sum of the two rolls is at most 7. Find P(B). dIn words, explain what “P(A|B)” represents. Find P(A|B). eAre A and B mutually exclusive events? Explain your answer in 1 - 3 complete sentences, including numerical justification. fAre A and B independent events? Explain your answer in 1 - 3 complete sentences, including numerical justification. A special deck of cards has 10 cards. Four are green, three are blue, and three are red. When a card is picked, the color of it is recorded. An experiment consists of first picking a card and then tossing a coin. aList the sample space. bLet A be the event that a blue card is picked first, followed by landing a head on the coin toss. Find P(A). cLet B be the event that a red or green is picked, followed by landing a head on the coin toss. Are the events A and B mutually exclusive? Explain your answer in 1 - 3 complete sentences, including numerical justification. dLet C be the event that a red or blue is picked, followed by landing a head on the coin toss. Are the events A and C mutually exclusive? Explain your answer in 1 - 3 complete sentences, including numerical justification. a { GH , GT , BH , BT , RH , RT } size 12{ lbrace ital "GH", ital "GT", ital "BH", ital "BT", ital "RH", ital "RT" rbrace } {} b 3 20 size 12{ { { size 8{3} } over { size 8{"20"} } } } {} cYes dNo An experiment consists of first rolling a die and then tossing a coin: aList the sample space. bLet A be the event that either a 3 or 4 is rolled first, followed by landing a head on the coin toss. Find P(A). cLet B be the event that a number less than 2 is rolled, followed by landing a head on the coin toss. Are the events A and B mutually exclusive? Explain your answer in 1 - 3 complete sentences, including numerical justification. An experiment consists of tossing a nickel, a dime and a quarter. Of interest is the side the coin lands on. aList the sample space. bLet A be the event that there are at least two tails. Find P(A). cLet B be the event that the first and second tosses land on heads. Are the events A and B mutually exclusive? Explain your answer in 1 - 3 complete sentences, including justification. a { ( HHH ) , ( HHT ) , ( HTH ) , ( HTT ) , ( THH ) , ( THT ) , ( TTH ) , ( TTT ) } size 12{ lbrace \( ital "HHH" \) , \( ital "HHT" \) , \( ital "HTH" \) , \( ital "HTT" \) , \( ital "THH" \) , \( ital "THT" \) , \( ital "TTH" \) , \( ital "TTT" \) rbrace } {} b 4 8 size 12{ { { size 8{4} } over { size 8{8} } } } {} cYes Consider the following scenario: Let P(C) = 0.4 Let P(D) = 0.5 Let P(C|D) = 0.6 aFind P(C AND D) . bAre C and D mutually exclusive? Why or why not? cAre C and D independent events? Why or why not? dFind P(C AND D) . eFind P(D|C). E size 12{E} {} and F size 12{F} {} mutually exclusive events. P(E)=0.4 size 12{P \( E \) =0 "." 4} {}; P(F)=0.5 size 12{P \( F \) =0 "." 5} {}. Find P(E∣F) size 12{P \( E \lline F \) } {}. 0 J size 12{J} {} and K size 12{K} {} are independent events. P(J | K) = 0.3 . Find P(J) size 12{P \( J \) } {} . U size 12{U} {} and V size 12{V} {} are mutually exclusive events. P(U)=0.26 size 12{P \( U \) =0 "." "26"} {}; P(V)=0.37 size 12{P \( V \) =0 "." "37"} {}. Find: aP(U AND V) = b P(U | V) = cP(U OR V) = a0 b 0 c0.63 Q size 12{Q} {} and R size 12{R} {} are independent events. P(Q) = 0.4 ; P(Q AND R) = 0.1 . Find P(R). Y size 12{Y} {} and Z size 12{Z} {} are independent events. a Rewrite the basic Addition Rule P(Y OR Z) = P(Y) + P(Z) - P(Y AND Z) using the information that Y and Z are independent events. b Use the rewritten rule to find P(Z) if P(Y OR Z) = 0.71 and P(Y) = 0.42 . b0.5 G size 12{G} {} and H size 12{H} {} are mutually exclusive events. P(G)=0.5 size 12{P \( G \) =0 "." 5} {}; P(H)=0.3 size 12{P \( H \) =0 "." 3} {}aExplain why the following statement MUST be false: P ( H ∣ G ) = 0 . 4 size 12{P \( H \lline G \) =0 "." 4} {} . bFind: P(H OR G). cAre G size 12{G} {} and H size 12{H} {} independent or dependent events? Explain in a complete sentence. The following are real data from Santa Clara County, CA. As of March 31, 2000, there was a total of 3059 documented cases of AIDS in the county. They were grouped into the following categories (Source: Santa Clara County Public H.D.): Homosexual/Bisexual IV Drug User* Heterosexual Contact Other Totals Female 0 70 136 49 ____ Male 2146 463 60 135 ____ Totals ____ ____ ____ ____ ____

* includes homosexual/bisexual IV drug users

Suppose one of the persons with AIDS in Santa Clara County is randomly selected. Compute the following:a P(person is female) = b P(person has a risk factor Heterosexual Contact) = c P(person is female OR has a risk factor of IV Drug User) = d P(person is female AND has a risk factor of Homosexual/Bisexual) = e P(person is male AND has a risk factor of IV Drug User) = f P(female GIVEN person got the disease from heterosexual contact) = gConstruct a Venn Diagram. Make one group females and the other group heterosexual contact. The completed contingency table is as follows: Homosexual/Bisexual IV Drug User* Heterosexual Contact Other Totals Female 0 70 136 49 255 Male 2146 463 60 135 2804 Totals 2146 533 196 174 3059

* includes homosexual/bisexual IV drug users

a 255 3059 b 196 3059 c 718 3059 size 12{ { { size 8{"718"} } over { size 8{"3059"} } } } {} d0 e 463 3059 f 136 196 Solve these questions using probability rules. Do NOT use the contingency table above. 3059 cases of AIDS had been reported in Santa Clara County, CA, through March 31, 2000. Those cases will be our population. Of those cases, 6.4% obtained the disease through heterosexual contact and 7.4% are female. Out of the females with the disease, 53.3% got the disease from heterosexual contact. aP(person is female) = bP(person obtained the disease through heterosexual contact) = cP(female GIVEN person got the disease from heterosexual contact) = dConstruct a Venn Diagram. Make one group females and the other group heterosexual contact. Fill in all values as probabilities. The following table identifies a group of children by one of four hair colors, and by type of hair. Hair Type Brown Blond Black Red Totals Wavy 20 15 3 43 Straight 80 15 12 Totals 20 215 aComplete the table above. bWhat is the probability that a randomly selected child will have wavy hair? cWhat is the probability that a randomly selected child will have either brown or blond hair? dWhat is the probability that a randomly selected child will have wavy brown hair? eWhat is the probability that a randomly selected child will have red hair, given that he has straight hair? fIf B is the event of a child having brown hair, find the probability of the complement of B. gIn words, what does the complement of B represent? b43215 c 120 215 size 12{ { { size 8{"120"} } over { size 8{"215"} } } } {} d20215 e12172 f 115 215 size 12{ { { size 8{"115"} } over { size 8{"215"} } } } {} A previous year, the weights of the members of the San Francisco 49ers and the Dallas Cowboys were published in the San Jose Mercury News. The factual data are compiled into the following table. Shirt# ≤ 210 211-250 251-290 290≤ 1-33 21 5 0 0 34-66 6 18 7 4 66-99 6 12 22 5 For the following, suppose that you randomly select one player from the 49ers or Cowboys.aFind the probability that his shirt number is from 1 to 33. bFind the probability that he weighs at most 210 pounds. cFind the probability that his shirt number is from 1 to 33 AND he weighs at most 210 pounds. dFind the probability that his shirt number is from 1 to 33 OR he weighs at most 210 pounds. eFind the probability that his shirt number is from 1 to 33 GIVEN that he weighs at most 210 pounds. fIf having a shirt number from 1 to 33 and weighing at most 210 pounds were independent events, then what should be true about P(Shirt# 1-33 | ≤ 210 pounds) ? Approximately 249,000,000 people live in the United States. Of these people, 31,800,000 speak a language other than English at home. Of those who speak another language at home, over 50 percent speak Spanish. (Source: U.S. Bureau of the Census, 1990 Census) Let: E = speak English at home; E' = speak another language at home; S = speak Spanish at home Finish each probability statement by matching the correct answer. Probability Statements Answers a. P(E') = i. 0.8723 b. P(E) = ii. > 0.50 c. P(S) = iii. 0.1277 d. P(S|E') = iv. > 0.0639 aiii bi civ dii The probability that a male develops some form of cancer in his lifetime is 0.4567 (Source: American Cancer Society). The probability that a male has at least one false positive test result (meaning the test comes back for cancer when the man does not have it) is 0.51 (Source: USA Today). Some of the questions below do not have enough information for you to answer them. Write “not enough information” for those answers. Let: C = a man develops cancer in his lifetime; P = man has at least one false positiveaConstruct a tree diagram of the situation. bP(C) = cP(P|C) = dP(P|C' ) = eIf a test comes up positive, based upon numerical values, can you assume that man has cancer? Justify numerically and explain why or why not. In 1994, the U.S. government held a lottery to issue 55,000 Green Cards (permits for non-citizens to work legally in the U.S.). Renate Deutsch, from Germany, was one of approximately 6.5 million people who entered this lottery. Let G = won Green Card. aWhat was Renate’s chance of winning a Green Card? Write your answer as a probability statement. bIn the summer of 1994, Renate received a letter stating she was one of 110,000 finalists chosen. Once the finalists were chosen, assuming that each finalist had an equal chance to win, what was Renate’s chance of winning a Green Card? Let F = was a finalist. Write your answer as a conditional probability statement. cAre G and F independent or dependent events? Justify your answer numerically and also explain why. dAre G and F mutually exclusive events? Justify your answer numerically and also explain why.P.S. Amazingly, on 2/1/95, Renate learned that she would receive her Green Card -- true story! a P ( G ) = 0 . 008 size 12{P \( G \) =0 "." "008"} {} b 0.5 cdependent dNo Three professors at George Washington University did an experiment to determine if economists are more selfish than other people. They dropped 64 stamped, addressed envelopes with $10 cash in different classrooms on the George Washington campus. 44% were returned overall. From the economics classes 56% of the envelopes were returned. From the business, psychology, and history classes 31% were returned. (Source: Wall Street Journal) Let: R = money returned; E = economics classes; O = other classesaWrite a probability statement for the overall percent of money returned. bWrite a probability statement for the percent of money returned out of the economics classes. cWrite a probability statement for the percent of money returned out of the other classes. dIs money being returned independent of the class? Justify your answer numerically and explain it. eBased upon this study, do you think that economists are more selfish than other people? Explain why or why not. Include numbers to justify your answer. The chart below gives the number of suicides estimated in the U.S. for a recent year by age, race (black and white), and sex. We are interested in possible relationships between age, race, and sex. We will let suicide victims be our population. (Source: The National Center for Health Statistics, U.S. Dept. of Health and Human Services) Race and Sex 1 - 14 15 - 24 25 - 64 over 64 TOTALS white, male 210 3360 13,610 22,050 white, female 80 580 3380 4930 black, male 10 460 1060 1670 black, female 0 40 270 330 all others TOTALS 310 4650 18,780 29,760 Do not include "all others" for parts (f), (g), and (i).aFill in the column for the suicides for individuals over age 64. bFill in the row for all other races. cFind the probability that a randomly selected individual was a white male. dFind the probability that a randomly selected individual was a black female. eFind the probability that a randomly selected individual was black fComparing “Race and Sex” to “Age,” which two groups are mutually exclusive? How do you know? gFind the probability that a randomly selected individual was male. hOut of the individuals over age 64, find the probability that a randomly selected individual was a black or white male. iAre being male and committing suicide over age 64 independent events? How do you know? c 22050 29760 size 12{ { {"22050"} over {"29760"} } } {} d 330 29760 size 12{ { {"330"} over {"29760"} } } {} e 2000 29760 size 12{ { { size 8{"2000"} } over { size 8{"29760"} } } } {} f 23720 29760 size 12{ { { size 8{"23720"} } over { size 8{"29760"} } } } {} g 5010 6020 size 12{ { { size 8{"5010"} } over { size 8{"6020"} } } } {} hBlack females and ages 1-14 iNo The next two questions refer to the following: The percent of licensed U.S. drivers (from a recent year) that are female is 48.60. Of the females, 5.03% are age 19 and under; 81.36% are age 20 - 64; 13.61% are age 65 or over. Of the licensed U.S. male drivers, 5.04% are age 19 and under; 81.43% are age 20 - 64; 13.53% are age 65 or over. (Source: Federal Highway Administration, U.S. Dept. of Transportation) Complete the following: aConstruct a table or a tree diagram of the situation. bP(driver is female) = cP(driver is age 65 or over | driver is female) = dP(driver is age 65 or over AND female) = eIn words, explain the difference between the probabilities in part (c) and part (d). fP(driver is age 65 or over) = gAre being age 65 or over and being female mutually exclusive events? How do you know Suppose that 10,000 U.S. licensed drivers are randomly selected. aHow many would you expect to be male? bUsing the table or tree diagram from the previous exercise, construct a contingency table of gender versus age group. cUsing the contingency table, find the probability that out of the age 20 - 64 group, a randomly selected driver is female. a5140 c0.49 Approximately 86.5% of Americans commute to work by car, truck or van. Out of that group, 84.6% drive alone and 15.4% drive in a carpool. Approximately 3.9% walk to work and approximately 5.3% take public transportation. (Source: Bureau of the Census, U.S. Dept. of Commerce. Disregard rounding approximations.) aConstruct a table or a tree diagram of the situation. Include a branch for all other modes of transportation to work. bAssuming that the walkers walk alone, what percent of all commuters travel alone to work? cSuppose that 1000 workers are randomly selected. How many would you expect to travel alone to work? dSuppose that 1000 workers are randomly selected. How many would you expect to drive in a carpool? Explain what is wrong with the following statements. Use complete sentences. aIf there’s a 60% chance of rain on Saturday and a 70% chance of rain on Sunday, then there’s a 130% chance of rain over the weekend. bThe probability that a baseball player hits a home run is greater than the probability that he gets a successful hit.

The next two questions refer to the following probability tree diagram which shows tossing an unfair coin FOLLOWED BY drawing one bead from a cup containing 3 red (R size 12{R} {}), 4 yellow (Y size 12{Y} {}) and 5 blue (B size 12{B} {}) beads. For the coin, P(H)=23 size 12{P \( H \) = { {2} over {3} } } {} and P(T)=13 size 12{P \( T \) = { {1} over {3} } } {} where H = "heads" and T = "tails”.

Find P(tossing a Head on the coin AND a Red bead) A 2 3 size 12{ { {2} over {3} } } {} B 5 15 size 12{ { {5} over {"15"} } } {} C 6 36 size 12{ { {6} over {"36"} } } {} D 5 36 size 12{ { {5} over {"36"} } } {} C Find P(Blue bead). A 15 36 size 12{ { {"15"} over {"36"} } } {} B 10 36 size 12{ { {"10"} over {"36"} } } {} C 10 12 size 12{ { {"10"} over {"12"} } } {} D 6 36 size 12{ { {6} over {"32"} } } {} A The next three questions refer to the following table of data obtained from www.baseball-almanac.com showing hit information for 4 well known baseball players. Suppose that one hit from the table is randomly selected. NAME Single Double Triple Home Run TOTAL HITS Babe Ruth 1517 506 136 714 2873 Jackie Robinson 1054 273 54 137 1518 Ty Cobb 3603 174 295 114 4189 Hank Aaron 2294 624 98 755 3771 TOTAL 8471 1577 583 1720 12351 Find P(hit was made by Babe Ruth).A 1518 2873 size 12{ { {"1518"} over {"2873"} } } {} B 2873 12351 size 12{ { {"2873"} over {"12351"} } } {} C 583 12351 size 12{ { {"583"} over {"12351"} } } {} D 4189 12351 size 12{ { {"4189"} over {"12351"} } } {} B Find P(hit was made by Ty Cobb | The hit was a Home Run) A 4189 12351 size 12{ { {"4189"} over {"12351"} } } {} B 1141 1720 size 12{ { {"1141"} over {"1720"} } } {} C 1720 4189 size 12{ { {"1720"} over {"4189"} } } {} D 114 12351 size 12{ { {"114"} over {"12351"} } } {} B Are the hit being made by Hank Aaron and the hit being a double independent events? A Yes, because P(hit by Hank Aaron | hit is a double) = P(hit by Hank Aaron) B No, because P(hit by Hank Aaron | hit is a double) ≠ P(hit is a double) C No, because P(hit is by Hank Aaron | hit is a double) ≠ P(hit by Hank Aaron) D Yes, because P(hit is by Hank Aaron | hit is a double) = P(hit is a double) C