This preview shows page 1. Sign up to view the full content.
Unformatted text preview: = 52.0 at 5% signiﬁcance level. (c) Suppose the manufacturer wishes to be at least 95% sure that his (point) estimate of µ will not involve an error
of more than 0.2 cm. How many more items must he sample to achieve this precision? II. Inference about a Normal Population mean when variance is unknown
1. How do the makers of Kleenex know how many tissues to put in a box? Researchers determine that 60 is the average
number of times people blow their nose during a cold by asking hundreds of customers to keep count of their Kleenex
use in diaries. Suppose a random sample of 250 Kleenex users yielded the following summary statistics on the number
of times they blew their noses when they had a cold: sample mean x = 57, sample standard deviation s = 26. Is
there suﬃcient evidence to dispute the researchers’ claim? Test at α = 0.05.
2. Twelve standard lengths of wool were extended over a given load before and after washing. The (after-less-before)
diﬀerences (cm) in the extensions were
1.7, −0.3, 0.3, 0.9, −0.4, 2.4, 1.1, 0.5, 1.2, 0.7, −0.5, 1.4
Test whether or not washing increases extensibility in general, at 5% signiﬁcance. III. Inference about a Population Proportion Based on Large Samples
1. To study the proportion of (p) of short-sighted students in a university, a sample of 40 students is taken of
whom 24 are found to be short-sighted.
Construct a 95% conﬁdence interval for p....
View Full Document