Body mass index of young women
• 18.22 Body mass index of young women. In Example 14.1
(page 287) we developed a 95% z confidence interval for the
mean body mass index (BMI) of women aged 20 to 29 years,
based on a national random sample of 654 such women. We
assumed there that the population standard deviation was
known to be σ = 7.5. In fact, the sample data had mean BMI =
26.8 and standard deviation s = 7.42. What is the 95% t
confidence interval for the mean BMI of all young women?
• Hint:
locate t* at df = n-1 & confidence level 95%
calculate margin of error m = t*
𝑠
𝑛
write out confidence interval CI = 𝑥 − 𝑏𝑎𝑟 ± 𝑚
Men of few words?
•
18.32 Men of few words? Researchers claim that women speak significantly more
words per day than men. One estimate is that a woman uses about 20,000 words
per day while a man uses about 7,000. To investigate such claims, one study used a
special device to record the conversations of male and female university students
over a four-day period. From these recordings, the daily word count of the 20 men
in the study was determined. Here are their daily word counts
Do the data give convincing evidence that the mean number of
words per day of men at this university differs from 7,000?
Hint: ◙ H0 : µ= 7000
◙ Calculate t-statistic :
Ha: µ ≠ 7000
After move out outlier 37,786, = 11,555.16, s = 6,095.015
◙ Using Table C to locate p-value by df = n-1 and t statistic
◙ Get conclusion