Department of Statistics STAV102 Business Statistics SICK TEST Date: 26 October 2024 Time: 120 min Examiner: Dr L Kepe, Ms S Alexander and Dr S Mangisa Marks: 65 Special Instructions: Part 1: Long Questions Complete the answers on the question paper in the space provided. 45 Marks You may use the back of the pages for rough work. Follow the instructions given on the multiple choice answer sheet Part 2: Multiple Choice provided. 20 Marks The use of pencil is preferable. All multiple choice answers are to be completed on the multiple choice answer sheet provided. 1. Answer ALL questions. 2. Round off your final answers to 3 decimal places. 3. Only financial/scientific calculators are allowed (no other electronic devices). 4. You may write in pencil (no remarks will be considered in this case). 5. Hand back ALL question papers and answer sheets when finished. Surname and Initials Student Number Question 1 2 3 4 5 6 7 8 Total Max 8 8 6 9 6 4 4 20 65 Mark 1 Part 1: Long Questions [45] Question 1 [8] When playing songs on the radio, it is important that the songs are neither too long nor too short. A sample of 30 songs, recorded by a certain artist is collected and the length of each song (in seconds) is recorded. The data are given in the table below: 181 208 201 199 243 192 152 185 162 180 198 179 195 231 186 249 139 207 185 172 (a) Complete the following frequency distribution table: Length of song (sec) [130, 150) [150, 170) [170, 190) [190, 210) [210, 230) [230, 250) Tally Frequency (f ) Relative frequency [5] Size of pie chart angle Cumulative Frequency (F ) (b) Construct a Ogive using the table in (a) and indicate the approximate value of the mode on the graph. Label all axes clearly. [3] s s s s s s s s s s s 2 Question 2 [8] An agronomist wants to determine the distribution of the sizes of potatoes in a crop at random locations. A random sample of 15 potatoes was collected and weighed (grams). The weights of the potatoes were recorded and are shown below: 230 215 224 223 245 237 237 199 215 207 228 213 222 228 237 (a) Calculate the arithmetic mean weight of the potatoes for the sample collected. [2] (b) Calculate the median weight of the potatoes for the sample collected. [3] (c) Calculate the mode weight of the potatoes for the sample collected. [3] (d) Comment on the skewness of the distributed weights of the potatoes (motivate your answer). [2] 3 Question 3 [6] A random sample of 50 first year students were asked to complete a test consisting of 20 basic mathematics questions. The frequency distribution for the number of questions the students answered incorrectly is given in the table below. # Incorrect Answers Frequency (f ) [0 - 4) 10 e [4 - 8) 22 e [8 - 12) 8 e [12 - 16) 6 e [16 - 20) 4 e (Use the blank cells in this table to aid in your calculations) (a) Calculate and interpret the first quartile of the number of questions that the students answered incorrectly. [3] (b) Determine the 85th percentile of the number of questions that the students answered incorrectly. [3] 4 Question 4 [9] Service calls received by a medical technologist constitute a Poisson process with a mean rate of 2.5 calls per hour. Calculate the probability that there will be; (a) no calls in a specific hour. [2] (b) at least one call in a specific hour. [2] (c) more than one call in 2 hours. [4] (d) How many calls would you expect in half hour period? [1] 5 Question 5 [6] A toy manufacturing company supplies batteries that last on average 18 hours with a variance of 9 (hours). If a battery life is normally distributed, what are the following probabilities? (a) that the battery life will be more than 12 hours. [3] (b) that the battery life will be between 13 and 19 hours [3] 6 Question 6 [4] The monthly profit generated by a medium-sized second-hand bookshop is thought to follow a normal distribution. A random sample of 9 such medium-sized second-hand bookshops reveals a sample mean of R13 000 with a sample standard deviation of R1 000. Construct a 99% confidence interval for the true population mean monthly profit of medium-size second-hand bookshops. Question 7 [4] A wood processing company wants to determine a 99% confidence interval for the standard deviation of the wood that is cut by their processing machine. A sample 30 logs was observed and it was found that the average lengths were 10.2 m with a standard deviation of 3.7 m. 7 Part 2: Multiple Choice Questions [20] 1. The relation between a parameter and a population is the same as the relation between a) Descriptive statistics and inferential statistics b) A dependent variable and an independent variable c) A statistic and a sample d) Quantitative and qualitative data e) A statistic and a variable [1] 2. The temperature (in ◦ C) in an air conditioned room would involve measurement on a(n) _____ scale. a) nominal b) ordinal c) interval d) ratio e) none of the above [1] 3. A scientist took daily measurements of the type of wildlife observed, the number of animals observed, amount of rain and the maximum temperature. Which of the following is a qualitative variable? a) Type of wildlife b) Number of animals observed c) Amount of rain d) Maximum temperature e) None of the above [1] 4. Statistical techniques that summarise, organise and simplify data are classified as _____ statistics. a) Population b) Sample c) Descriptive d) Inferential e) Classical [1] 5. A sample of 30 individuals who smoke cigarettes was collected. Each individual was classified according to how many cigarettes they smoked per day as either a “heavy smoker”, a “average smoker”, a “light smoker”, or a “social smoker”. 12 of the sampled individuals were classified as “heavy smokers”, 7 as “light smokers”, 3 as “average smokers” and the rest were classified as “social smokers”. If a pie chart were to be made for this data, what would be the angle size for the “social smokers” category in the pie chart? a) 84◦ b) 36◦ c) 96◦ d) 144◦ e) none of the above [1] 6. Which of the following graphical representations of data is used to graphically represent qualitative data? a) histograms 8 b) frequency polygons c) ogives d) pie charts e) none of the above [1] For questions (7) to (9) consider the following scenario. A random sample of 8 fraudulent transactions identified by a bank were investigated and the values (in R) of the fraudulent transactions are given below 350 690 1000 540 125 600 220 1500 7. Calculate the mean value of the data above. a) 456.38 b) 717.86 c) 628.13 d) 570.00 e) None of the above / cannot be calculated. [1] 8. Calculate the median value of the data above. a) 570.00 b) 600.00 c) 540.00 d) 575.00 e) None of the above / cannot be calculated [1] 9. Calculate the first quartile of the data above. a) 220.00 b) 350.00 c) 285.00 d) 252.50 e) None of the above / cannot be calculated [1] 10. Consider the histogram below and select the correct order for the mean, median and mode. 9 a) I = Mode; II = Mean; III = Median b) I = Median; II = Mean; III = Mode c) I = Mean; II = Median; III = Mode d) I = Mean; II = Mode; III = Median e) I = Mode; II = Median; III = Mean [1] 11. The following table provides a complete point probability distribution for the random variable X. Calculate the missing value indicated by ???. x P (X = x) 0 0.25 1 ??? 2 0.05 3 0.06 4 0.53 a) 0.75 b) 0.56 c) 0.14 d) 0.11 e) None of the above / cannot be calculated. For questions (12) and (13) consider the following scenario. The following table provides a complete point probability distribution for the random variable X. x P (X = x) 0 0.10 2 0.23 4 0.42 6 0.20 8 0.05 12. What is E [X]? a) 3.75 b) 3.84 c) 4.00 d) 0.23 e) none of the above [1] 13. What is P (X > 8)? a) 0.05 b) 0.95 c) 0.00 d) 0.10 e) none of the above [1] 14. Suppose that X has a binomial distribution with n = 3 and p = 0.62. Calculate P (X ≤ 0). a) 0.055 b) 0.945 c) 0.620 d) 0.830 e) None of the above / cannot be calculated. [1] 15. Suppose it is known that the height of first year students in cm (X) has a normal distribution with µ = 100 and σ = 15. A sample of 9 students is collected and their heights measured. Which of the following statements is correct? 10 a) X̄ ∼ N (100; 15) b) X̄ ∼ N (100; 1.67) c) X̄ ∼ N (100; 25) d) X̄ ∼ (100; 5) e) none of the above [1] 16. Which of the following properties of the standard normal distribution (Z) is correct? Note: z is any real number, a and b are positive real numbers. a) P (−a < Z < b) = P (Z < b) + P (Z < a) − 1 b) P (Z = z) > 0 c) P (a < Z < b) = P (Z < a) − P (Z < b) d) P (Z > z) = 1 − P (Z < −z) e) none of the above [1] 17. The sampling error of the mean is defined as a) 1 − p b) x − xi c) x̄ − p̂ d) x̄ − µ e) none of the above [1] 18. Suppose that a random variable Y has a normal distribution with a mean of 2 and a standard deviation of 0.95. Calculate P (Y > 3.1). a) 0.8599 b) 0.0485 c) 0.1292 d) 0.1401 e) none of the above [1] For questions (19) and (20) consider the following scenario. A financial analyst is interested in the average return on a portfolio. In order to report this average return, a confidence interval must be calculated. 19. In which of the following scenarios would the analyst use the standard normal distribution / table to calculate the confidence interval for the mean return? a) When n < 30, σ is known and the data are normally distributed. b) When n < 30, σ is unknown and the data are not normally distributed. c) When n < 30, σ is unknown and the data are normally distributed. d) When n < 30, σ is known and the data are not normally distributed. e) none of the above 11 [1] 20. Suppose now that the analyst uses the standard normal distribution to calculate the confidence interval for the mean return. Which of the following intervals will be the narrowest? a) A 99% confidence interval b) A 97.5% confidence interval c) A 95% confidence interval d) A 90% confidence interval e) All the confidence intervals are equal in length 12 [1] STAV102 Formula Sheet ( k = 1 + 3.3log (n) = 1 + 3.3 ln (n) ln (10) ) xmax − xmin ∑ k n = fi c = Rel. freq = x̄ = x̄ = fi n n 1∑ xi n i=1 ∑ f i xi ∑ ∑ s 2 = s2 = fi √ ∑ s = √∑ s = √∑ s = CV Me Mo Q1 ∑ ∑ x2i − n1 ( xi )2 (xi − x̄)2 = n−1 n−1 ∑ 2 1 ∑ 2 fi xi − n ( fi xi ) n−1 (xi − x̄)2 n−1 ∑ x2i − n1 ( xi )2 n−1 ∑ fi x2i − n1 ( fi xi )2 n−1 s × 100 x̄ ) ( c n2 − Fi−1 = li + fi ( ) c (fi − fi−1 ) = li + (fi − fi−1 ) + (fi − fi+1 ) (n ) c 4 − Fi−1 = li + fi = ( c Q 3 = li + 3n 4 − Fi−1 ) fi IQR = Q3 − Q1 LL = Q1 − 1.5 · IQR U L = Q3 + 1.5 · IQR ( np ) c 100 − Fi−1 Pp = l i + fi f P (A) = n P (A ∪ B) = P (A) + P (B) − P (A ∩ B) P (A ∩ B) P (A|B) = P (B) P (A) = P (B1 ) P (A|B1 ) + · · · + P (Bn ) P (A|Bn ) P (Bk ) P (A|Bk ) P (Bk |A) = P (B1 ) P (A|B1 ) + · · · + P (Bn ) P (A|Bn ) P (A ∩ B) = P (A) P (B|A) P (A ∩ B) = P (A) P (B) n! n Cr = r! (n − r)! 13 E [X] = µ = V [X] = σ 2 = P (X = x) = ∑ ∑ xp (x) x2 p (x) − n Cr p x (∑ xp (x) )2 (1 − p)n−x E [X] = np V [X] = np (1 − p) µx e−µ P (X = x) = x! E [X] = V [X] = µ P (Z < −z) = P (Z > z) P (Z > z) = 1 − P (Z ≤ z) X −µ Z = σ σ σX̄ = √ n X −µ Z = σX̄ X −µ Z = σ/√n X p̂ = n √ σp = Z = Z = p (1 − p) n p̂ − p σp p̂ − p √ [ p(1−p) n ] σ x̄ ± z1−α/2 √ n [ ] s = x̄ ± z1−α/2 √ n CI (µ)1−α = CI (µ)1−α [ CI (µ)1−α = s x̄ ± tn−1;1−α/2 √ n √ CI (p)1−α = p̂ ± z1−α/2 ( CI σ 2 [ ) 1−α = ] p̂(1 − p̂) n (n − 1) s2 (n − 1) s2 ; χ2n−1;1−α/2 χ2n−1;α/2 ( ) z1−α/2 σ 2 n = e ( ) z1−α/2 2 n = p(1 − p) e 14 ] z 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 0.00 0.5000 0.5398 0.5793 0.6179 0.6554 0.6915 0.7257 0.7580 0.7881 0.8159 0.8413 0.8643 0.8849 0.9032 0.9192 0.9332 0.9452 0.9554 0.9641 0.9713 0.9772 0.9821 0.9861 0.9893 0.9918 0.9938 0.9953 0.9965 0.9974 0.9981 0.9987 0.9990 0.9993 0.9995 0.9997 0.01 0.5040 0.5438 0.5832 0.6217 0.6591 0.6950 0.7291 0.7611 0.7910 0.8186 0.8438 0.8665 0.8869 0.9049 0.9207 0.9345 0.9463 0.9564 0.9649 0.9719 0.9778 0.9826 0.9864 0.9896 0.9920 0.9940 0.9955 0.9966 0.9975 0.9982 0.9987 0.9991 0.9993 0.9995 0.9997 Standard Normal Probabilities P (Z ≤ z) 0.02 0.03 0.04 0.05 0.06 0.07 0.5080 0.5120 0.5160 0.5199 0.5239 0.5279 0.5478 0.5517 0.5557 0.5596 0.5636 0.5675 0.5871 0.5910 0.5948 0.5987 0.6026 0.6064 0.6255 0.6293 0.6331 0.6368 0.6406 0.6443 0.6628 0.6664 0.6700 0.6736 0.6772 0.6808 0.6985 0.7019 0.7054 0.7088 0.7123 0.7157 0.7324 0.7357 0.7389 0.7422 0.7454 0.7486 0.7642 0.7673 0.7704 0.7734 0.7764 0.7794 0.7939 0.7967 0.7995 0.8023 0.8051 0.8078 0.8212 0.8238 0.8264 0.8289 0.8315 0.8340 0.8461 0.8485 0.8508 0.8531 0.8554 0.8577 0.8686 0.8708 0.8729 0.8749 0.8770 0.8790 0.8888 0.8907 0.8925 0.8944 0.8962 0.8980 0.9066 0.9082 0.9099 0.9115 0.9131 0.9147 0.9222 0.9236 0.9251 0.9265 0.9279 0.9292 0.9357 0.9370 0.9382 0.9394 0.9406 0.9418 0.9474 0.9484 0.9495 0.9505 0.9515 0.9525 0.9573 0.9582 0.9591 0.9599 0.9608 0.9616 0.9656 0.9664 0.9671 0.9678 0.9686 0.9693 0.9726 0.9732 0.9738 0.9744 0.9750 0.9756 0.9783 0.9788 0.9793 0.9798 0.9803 0.9808 0.9830 0.9834 0.9838 0.9842 0.9846 0.9850 0.9868 0.9871 0.9875 0.9878 0.9881 0.9884 0.9898 0.9901 0.9904 0.9906 0.9909 0.9911 0.9922 0.9925 0.9927 0.9929 0.9931 0.9932 0.9941 0.9943 0.9945 0.9946 0.9948 0.9949 0.9956 0.9957 0.9959 0.9960 0.9961 0.9962 0.9967 0.9968 0.9969 0.9970 0.9971 0.9972 0.9976 0.9977 0.9977 0.9978 0.9979 0.9979 0.9982 0.9983 0.9984 0.9984 0.9985 0.9985 0.9987 0.9988 0.9988 0.9989 0.9989 0.9989 0.9991 0.9991 0.9992 0.9992 0.9992 0.9992 0.9994 0.9994 0.9994 0.9994 0.9994 0.9995 0.9995 0.9996 0.9996 0.9996 0.9996 0.9996 0.9997 0.9997 0.9997 0.9997 0.9997 0.9997 Standard Normal Critical Values α (1 − α) α z1−α z1−α/2 2 0.9 0.1 0.05 1.282 1.645 0.95 0.05 0.025 1.645 1.960 0.98 0.02 0.01 2.054 2.326 0.99 0.01 0.005 2.326 2.576 15 0.08 0.5319 0.5714 0.6103 0.6480 0.6844 0.7190 0.7517 0.7823 0.8106 0.8365 0.8599 0.8810 0.8997 0.9162 0.9306 0.9429 0.9535 0.9625 0.9699 0.9761 0.9812 0.9854 0.9887 0.9913 0.9934 0.9951 0.9963 0.9973 0.9980 0.9986 0.9990 0.9993 0.9995 0.9996 0.9997 0.09 0.5359 0.5753 0.6141 0.6517 0.6879 0.7224 0.7549 0.7852 0.8133 0.8389 0.8621 0.8830 0.9015 0.9177 0.9319 0.9441 0.9545 0.9633 0.9706 0.9767 0.9817 0.9857 0.9890 0.9916 0.9936 0.9952 0.9964 0.9974 0.9981 0.9986 0.9990 0.9993 0.9995 0.9997 0.9998 df 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 35 40 45 50 60 70 80 90 100 ∞ 0.75 1.000 0.816 0.765 0.741 0.727 0.718 0.711 0.706 0.703 0.700 0.697 0.695 0.694 0.692 0.691 0.690 0.689 0.688 0.688 0.687 0.686 0.686 0.685 0.685 0.684 0.684 0.684 0.683 0.683 0.683 0.682 0.681 0.680 0.679 0.679 0.678 0.678 0.677 0.677 0.674 Students t-Distribution Critical Values Lower tail probability (1 − α) 0.9 0.95 0.975 0.99 0.995 0.9975 3.078 6.314 12.706 31.821 63.657 127.321 1.886 2.920 4.303 6.965 9.925 14.089 1.638 2.353 3.182 4.541 5.841 7.453 1.533 2.132 2.776 3.747 4.604 5.598 1.476 2.015 2.571 3.365 4.032 4.773 1.440 1.943 2.447 3.143 3.707 4.317 1.415 1.895 2.365 2.998 3.499 4.029 1.397 1.860 2.306 2.896 3.355 3.833 1.383 1.833 2.262 2.821 3.250 3.690 1.372 1.812 2.228 2.764 3.169 3.581 1.363 1.796 2.201 2.718 3.106 3.497 1.356 1.782 2.179 2.681 3.055 3.428 1.350 1.771 2.160 2.650 3.012 3.372 1.345 1.761 2.145 2.624 2.977 3.326 1.341 1.753 2.131 2.602 2.947 3.286 1.337 1.746 2.120 2.583 2.921 3.252 1.333 1.740 2.110 2.567 2.898 3.222 1.330 1.734 2.101 2.552 2.878 3.197 1.328 1.729 2.093 2.539 2.861 3.174 1.325 1.725 2.086 2.528 2.845 3.153 1.323 1.721 2.080 2.518 2.831 3.135 1.321 1.717 2.074 2.508 2.819 3.119 1.319 1.714 2.069 2.500 2.807 3.104 1.318 1.711 2.064 2.492 2.797 3.091 1.316 1.708 2.060 2.485 2.787 3.078 1.315 1.706 2.056 2.479 2.779 3.067 1.314 1.703 2.052 2.473 2.771 3.057 1.313 1.701 2.048 2.467 2.763 3.047 1.311 1.699 2.045 2.462 2.756 3.038 1.310 1.697 2.042 2.457 2.750 3.030 1.306 1.690 2.030 2.438 2.724 2.996 1.303 1.684 2.021 2.423 2.704 2.971 1.301 1.679 2.014 2.412 2.690 2.952 1.299 1.676 2.009 2.403 2.678 2.937 1.296 1.671 2.000 2.390 2.660 2.915 1.294 1.667 1.994 2.381 2.648 2.899 1.292 1.664 1.990 2.374 2.639 2.887 1.291 1.662 1.987 2.368 2.632 2.878 1.290 1.660 1.984 2.364 2.626 2.871 1.282 1.645 1.960 2.326 2.576 2.807 16 0.999 318.309 22.327 10.215 7.173 5.893 5.208 4.785 4.501 4.297 4.144 4.025 3.930 3.852 3.787 3.733 3.686 3.646 3.610 3.579 3.552 3.527 3.505 3.485 3.467 3.450 3.435 3.421 3.408 3.396 3.385 3.340 3.307 3.281 3.261 3.232 3.211 3.195 3.183 3.174 3.090 df 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 40 50 60 70 80 0.005 0 0.01 0.072 0.21 0.41 0.68 0.99 1.34 1.73 2.16 2.6 3.07 3.57 4.07 4.6 5.14 5.7 6.26 6.84 7.43 8.03 8.64 9.26 9.89 10.52 11.16 11.81 12.46 13.12 13.79 20.71 27.99 35.53 43.28 51.17 0.01 0 0.02 0.115 0.3 0.55 0.87 1.24 1.65 2.09 2.56 3.05 3.57 4.11 4.66 5.23 5.81 6.41 7.01 7.63 8.26 8.9 9.54 10.2 10.86 11.52 12.2 12.88 13.56 14.26 14.95 22.16 29.71 37.48 45.44 53.54 χ2 distribution critical values (1 − α) 0.025 0.05 0.1 0.9 0.95 0.001 0.004 0.016 2.71 3.84 0.051 0.103 0.211 4.61 5.99 0.216 0.35 0.58 6.25 7.81 0.48 0.71 1.06 7.78 9.49 0.83 1.15 1.61 9.24 11.07 1.24 1.64 2.2 10.64 12.59 1.69 2.17 2.83 12.02 14.07 2.18 2.73 3.49 13.36 15.51 2.7 3.33 4.17 14.68 16.92 3.25 3.94 4.87 15.99 18.31 3.82 4.57 5.58 17.28 19.68 4.4 5.23 6.3 18.55 21.03 5.01 5.89 7.04 19.81 22.36 5.63 6.57 7.79 21.06 23.68 6.26 7.26 8.55 22.31 25 6.91 7.96 9.31 23.54 26.3 7.56 8.67 10.09 24.77 27.59 8.23 9.39 10.86 25.99 28.87 8.91 10.12 11.65 27.2 30.14 9.59 10.85 12.44 28.41 31.41 10.28 11.59 13.24 29.62 32.67 10.98 12.34 14.04 30.81 33.92 11.69 13.09 14.85 32.01 35.17 12.4 13.85 15.66 33.2 36.42 13.12 14.61 16.47 34.38 37.65 13.84 15.38 17.29 35.56 38.89 14.57 16.15 18.11 36.74 40.11 15.31 16.93 18.94 37.92 41.34 16.05 17.71 19.77 39.09 42.56 16.79 18.49 20.6 40.26 43.77 24.43 26.51 29.05 51.81 55.76 32.36 34.76 37.69 63.17 67.5 40.48 43.19 46.46 74.4 79.08 48.76 51.74 55.33 85.53 90.53 57.15 60.39 64.28 96.58 101.88 17 0.975 5.02 7.38 9.35 11.14 12.83 14.45 16.01 17.53 19.02 20.48 21.92 23.34 24.74 26.12 27.49 28.85 30.19 31.53 32.85 34.17 35.48 36.78 38.08 39.36 40.65 41.92 43.19 44.46 45.72 46.98 59.34 71.42 83.3 95.02 106.63 0.99 6.63 9.21 11.34 13.28 15.09 16.81 18.48 20.09 21.67 23.21 24.72 26.22 27.69 29.14 30.58 32 33.41 34.81 36.19 37.57 38.93 40.29 41.64 42.98 44.31 45.64 46.96 48.28 49.59 50.89 63.69 76.15 88.38 100.43 112.33 0.995 7.88 10.6 12.84 14.86 16.75 18.55 20.28 21.95 23.59 25.19 26.76 28.3 29.82 31.32 32.8 34.27 35.72 37.16 38.58 40 41.4 42.8 44.18 45.56 46.93 48.29 49.64 50.99 52.34 53.67 66.77 79.49 91.95 104.21 116.32