Question

(3 points) The Highway Safety Department wants to study the driving habits of individuals. A sample of 43 cars traveling on a particular stretch of highway revealed an average speed of 67.7 miles per hour with a standard deviation of 10 miles per hour. Round to 4 decimal places. 1. Calculate a 90% confidence interval for the true mean speed of all cars on this particular stretch of highway. (65.135 , 70.265 ) 2. What sample size is needed to estimate the true average speed to within 2.5 mph at 90% confidence? Note: For consistency's sake, round your t* value to 3 decimal places before calculating the necessary sample size. Choose n= Help Entering Answers Preview My Answers Submit Answers Results for this submission Entered Answer Preview Result 65.135 65.135 correct 70.265 70.265 correct 43 incorrect

Answer 1

Date. solution). Given that, Ž= 67.7 s- lo n= 43 df = n-1 =43-1=42 At ao olo confidence level the t is dol-9900 Zal-0.99 -On 10 A = 0.1 = 6.05 taje; dfatoos : 42 = 1.682 At - 90 % confidence X £ ta 12', dfxs interual for uis 6717 I 1.682X 10 43 67.7 + 2.565 (65.135, 70.265) - A qo do confidence interval for ulc (165.135 1,[ 70.2851)

E 2.5 6=10 1 df = n-1 =43-1=22 At do % confidence level the tis asi-o oo al-0.90 = 0.10 2012 -0.050 ta 121, alfa tooos! 42 = 11682 Sample size= |212 46 na |1682x10 T1-682X10 2 .5 n = 45.266 n = 46 sample size n= 46