1. A sample of 49 observations is taken from a normal population with a standard deviation of 10. The sample mean is 55. Determine the 99 persen confidence interval for the population mean Soal dan jawab penaksiran no 1
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 1 page 297)

  2. A sample of 81 observations is taken from a normal distribution with a standard deviation of 5. The sample mean is 40. Detremine the 95% confidence interval for the population mean Soal dan jawab penaksiran no 2
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise2 page 297)
  3. A research firm conducted a survey to determine the mean amount steady smokers spend on cigarettes during a week. They found the distribution of amount spend per week followed the normal distribution with standard deviation of $ 5. A sampel of 49 steady smokers revealed that
    (a) What is the point estimate of the population mean?
    (b) Using the 95 percent level of confidence, determine the confidence interval for Soal dan jawab penaksiran no 3
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 5 page 297)

  4. The owner of Britten’s Egg Farm wants to estimate the mean number of eggs laid per chiken. A Sample of 20 chickens shows they laid an average of 20 eggs per month with a standard deviation of 2 eggs per month
    (a) What is the value of population mean? What is the best estimates of this value
    (b) Explain why we need to use the t distribution. What assumption do you need to make?
    (c)For a 95 % confidence level, what is the value of t(
    d) Develop a 95 percent confidence interval for the population mean
    (e)Would it be reasonable to conclude that the population mean is 21 eggs ? what about 25 eggs Soal dan jawab penaksiran no 4
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 11 page 304)

  5. The owner of the West End Kwick Fill Gas Station wishes to determine the proportion of customers who use a credit card or debit card to pay at the pump. He surveys 100 customers and find that 80 paid at the pump
    (a) Estimate the value of the population proportion
    (b)Develop a 95 % confidence interval for the proportion
    (c) Interpret your findings Soal dan jawab penaksiran no 5
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 15 page 308)

  6. Ms Maria Wilson a considering running for mayor of the town of Bear Gulch, Montana. Before completing the petitions, she decides to conduct a survey of voters in Bear Gulch. A sample of 400 voters reveals that 300 would support her in the November election
    (a) Estimate the value of population proportion
    (b) Develop a 99 percent confidence interval for the population proportion
    (c) Interpret your finding Soal dan jawab penaksiran no 6
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 16 page 308)

  7. The attendance at the savannah Colts minor league baseball game last night was 400. A random sampel of 50 of those in attendance revealed that the mean number of soft drinks comsumed per person wa 1.86 with stnadradr deviation of 0.50. Develop of a 99 percent confidence interval for the mean number of soft drinks comsumed per person Soal dan jawab penaksiran no 7
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 21 page 310)

  8. A population is estimated to have a standard deviation of 10. We want to estimate the population mean within 2, within a 95 percent level of confidence. Hor large a sample is required? Soal dan jawab penaksiran no 8
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 23 page 313

  9. A survey is being planned to determine the mean amount of time corporation executives watch television. A pilot survey indicated that the mean per week is 12 hours, with a standard deviation of 3 hours. It is desired to estimate the mean viewing time within one-quarter hour. The 95 percent level of confidence is to be used. How many executives should be surveyed? Soal dan jawab penaksiran no 9
    (Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 27 page 313

10. Suppose the US president wants an estimate of the proportion of the population who support his current policy toward revisions in the social security system. The president want to estimate to be within 0.04 of the true population. Assume 1 95 percent level of confidence. The president’s political advisors estimated the proportion supporting the current policy to be 0.60
(a) How large a sample is required
(b)How large a sample would be necessary if no estimate were available for the proportion supporting current policy Soal dan jawab penaksiran no 10
(Lind, Marchal, Wathen., Statistical Techniques in Business and Economics., Mac Graw Hill., Fourteenth edition., Exercise 29 page 313

11. Sebuah perusahaan memproduksi bohlam yang umurnya kira-kira menyebar normal dengan simpangan baku 40 jam. Bila suatu contoh acak 30 bohlam mencapai umur rata-rata 780 jam, buat selang kepercayaan 96% bagi nilai tengah populasi umur bohlam yang diproduksi perusahaan itu
(Ronald E Walpole., Pengantar Statistika., PT gramedia Pustaka Utama, Jakarta, Edisi ke 3, Soal-soal latihan halaman 256, nomor 3) Soal dan jawab penaksiran no 11

12. Berapa besarnya contoh yang diperlukan dalam soal no 11 bila kita ingin percaya 96% bahwa rata-rata contoh kita berada dalam 10 jam dari nilai tengah yang sebenarnya ?  Soal dan jawab penaksiran no 12
(Ronald E Walpole., Pengantar Statistika., PT gramedia Pustaka Utama, Jakarta, Edisi ke 3, Soal-soal latihan halaman 257, nomor 7)

13. Suatu mesin minuman diatur sedemikian rupa sehingga banyaknya minuman yang dikeluarkannya berdistribusi hamper normal dengan simpangan baku 1.5 desiliter.
a)    Hitunglah selang kepercayaan 95% untuk rataan semua minuman yang dikeluarkan mesin tersebut bila sampel acak 36 cangkir minuman berisi rata-rata 22.5 desiliter
b)    Berapa besarnya sampel yang diperlukan bila kita ingin percaya 95% bahwa rata-rata sampel berada dalam 0.3 desiliter dari nilai tengah sebenarnya soal dan jawab penaksiran no 13
(Ronald E Walpole., Pengantar Statistika., PT gramedia Pustaka Utama, Jakarta, Edisi ke 3, Soal-soal latihan halaman 256, nomor 4 dan no 8)

14. Dari 25 mahasiswa yang diambil secara acak, tinggi rata-ratanya mencapai 174,5 cm dengan simpangan baku 6.9 cm.
(a)  Buat selang kepercayaan 98% bagi nilai tengah tinggi semua mahasiswa
(b)  Dengan kepercayaan 98%, apa yang dapat kita nyatakan mengenai kemungkinan besarnya galat bila kita menduga nilai tengah tinggi semua mahasiswa sebesar 174.5 cm?
(c)  Berapa sampel yang dibutuhkan bila kita ingin percaya bahwa rata-rata sampel berada dalam 2 cm dari nilai rata-rata tinggi yang sebenarnya soal dan jawab penaksiran no 14
(Ronald E Walpole., Pengantar Statistika., PT gramedia Pustaka Utama, Jakarta, Edisi ke 3, Soal-soal latihan halaman 256, nomor 5)

15. Dari suatu sampel acak 1000 rumah di sebuah kota, ditemukan bahwa 628 rumah menggunakan pemanas gas alam.
(a)  Buat selang kepercayaan 98% bagi proporsi rumah-rumah di kota tersebut yang menggunakan pemas gas alam
(b)  Berapa besar sampel yang diperlukan bila kita ingin percaya 98% bahwa proporsi sampel yang diperoleh terletak dalam jarak yang tidak lebih 0.05 dari proporsi populasi yang sebenarnya  soal dan jawab penaksiran no 15
(Ronald E Walpole., Pengantar Statistika., PT gramedia Pustaka Utama, Jakarta, Edisi ke 3, Soal-soal latihan halaman 264, nomor 3 dan nomor 7)

16. Becaude the owner of the Bard’s Nook, a recently openede raestaurant, has had difficulty estimating the quantuti of food to be prepared each evening, he decide to determine the mean number of customers served each night. He selected a sampel of 30 night, which resulted in a mean of 71. The population standard deviation has been established as 3.76.
(a) Give an interval estimate that has a 68.3 percent probability of including the population mean
(b) Give an interval estimate that has a 99.7 percent chance of including the population mean solution of Estimation Assigment no 16
(Richard I. Levin, David S. Rubin., Statistics for Management., Prentice Hall International, Sevent Edition.,page 357, number 7-15)

17. Twelve bank tellers were randomly sampled and it was determied tyhey made an average of 3.6 errors per day with a sample standard deviation of 0.42 error. Construct a 90 percent confidence interval for the population mean of errors per day. What assumption is implied about the number of a errors bank tellers make? solution of Estimation Assigment no 17
(Richard I. Levin, David S. Rubin., Statistics for Management., Prentice Hall International, Sevent Edition.,page 378, number 7-49)

18. The Westview High School nurse is interested in knowing the average height of seniors at this school, but she does not have enough time to record of all 430 seniors. She randomly select 48 students and she finds the sampel mean to be 64.5 inches and the stanadard deviation to be 2.3 inches.
(a) Find the estimated standard error of the mean
(b) Construct a 90 percent confidence interval for the mean solution of Estimation Assigment no 18
(Richard I. Levin, David S. Rubin., Statistics for Management., Prentice Hall International, Sevent Edition.,page 365, number 7-30)

19. Food Tiger, a local grocery store, sells generic garbage bags has received quite a few complaints about the strength of theese bags. It seems that the generic bags are weaker than the name brand competitors’s bags and therefore, break more often. Jhon C. Tiger, VP in charge of purcagsing is interested in determine tha average maximum weight that can be put into one of the generic  bags without is breaking. If the standard devaition of garbage breaking wiegh is 1.2 lb, determine the number of bags tha must be tested in order for Mr Tiger to ben 95% percent confident that the sample average breaking weight is within 0.5 lb of the true average? solution of Estimation Assigment no 19
(Richard I. Levin, David S. Rubin., Statistics for Management., Prentice Hall International, Sevent Edition.,page 383, number 7-56)