HW4 - STAT 350 Homework #4 - SOLUTION Text Exercises...

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STAT 350 – Homework #4 - SOLUTION Text Exercises Chapter 7 problems #8(a,b,c), 12, 18, 30 7.8 a. 2.33 b. 1.44 c. 1.15 7.12 a. 1.27 9.15 1.96 56 ⎛⎞ ± ⎜⎟ ⎝⎠ = (8.8174, 9.4826) b. 1.71 3.08 2.575 61 ± = (2.5162, 3.6438) This interval is wider because the confidence level is higher (and because the sample standard deviation is larger) 7.18 31.5 382.1 1.645 390.74 36 += 7.30 () 22 4.89 6.43 26.99 35.76 1.96 68 74 −± + = (-10.6401, -6.8999) Note: (6.8999, 10.6401) is also acceptable, this is just the 95% CI for 21 μ instead of 12 Then answer the following Problems 1. You want to calculate the mean gas mileage (in mpg) for a new model of car. You want to determine the sample size needed to be at least 86% certain that your sample mean will be within 0.5 mpg of the true mean. From past experience, you believe that the standard deviation in mileage of these cars is 4.6 mpg. What is the minimum number of cars you will need in your sample? 2 2 /2 1.48 4.6 0.5 zs n B α × ⎡⎤ == ⎢⎥ ⎣⎦ =185.395 Because I said we want to be at least 86% certain, we want to round up – we will need at least 186 cars in the sample

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This note was uploaded on 03/09/2010 for the course STAT 350 taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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HW4 - STAT 350 Homework #4 - SOLUTION Text Exercises...

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