A study was conducted to test the effect of a new ecofriendly alternative to roa
ID: 3428451 • Letter: A
Question
A study was conducted to test the effect of a new ecofriendly alternative to road salt on automobile traction. A random sample of the skidding distance (in meters) of cars along the same stretch of highway during a cold, icy winter day was obtained. The data are given in the following table.
488
352
455
199
288
406
575
435
545
385
299
433
183
260
273
402
310
313
143
424
Suppose the distribution of skidding distances is normal. Find a 95% confidence interval for the true mean skidding distance.
488
352
455
199
288
406
575
435
545
385
299
433
183
260
273
402
310
313
143
424
Explanation / Answer
sample mean=358.4
sample standard deviation =117.19278
sample size n=20
The degree of freedom =n-1=20-1=19
Given a=0.05, t(0.025, df=19) =2.09 (from student t table)
So a 95% confidence interval for the true mean skidding distance is
xbar +/- t*s/vn
--> 358.4 +/- 2.09*117.19278/sqrt(20)
--> (303.6313, 413.1687)
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