HOMEWORK QUESTIONS
SECTION 8.3
ESTIMATING A POPULATION
MEAN
ONE-SAMPLE
Z INTERVAL FOR A POPULATION MEAN

𝑥 ± 𝑧∗
𝜎
𝑛
As long as the Random, Normal, and
Independent conditions are met…This is your
confidence interval!
 We use this when we know 𝜎

CHOOSING A SAMPLE SIZE

Now that we know 𝜎 …

𝑧∗

𝜎
𝑛
≤ 𝑀𝐸
Ex: Obtaining monkeys is time-consuming and expensive, so
researchers want to know the minimum number of monkeys
needed to generate a satisfactory estimate of cholesterol levels
for a study. They want their estimate to be within 1 mg/dl of the
true value of 𝜇 at a 95% confidence interval.
WHEN 𝜎 IS UNKNOWN…T DISTRIBUTIONS
WHEN 𝜎 IS UNKNOWN…T DISTRIBUTIONS
𝑥−𝜇

𝑡=

𝑑𝑓 = 𝑛 − 1
𝑠𝑥
𝑛
ONE-SAMPLE T INTERVAL FOR A
POPULATION MEAN


𝑥 ± 𝑡∗
𝑠𝑥
𝑛
Use when the population is Normal or the sample
size is large enough (𝑛 ≥ 30) and the population
is at least 10 times the sample size.
T PROCEDURES: THE NORMAL CONDITION


Sample size less than 30 – use t if the data
appear close to Normal (roughly symmetric,
single peak, no outliers). Do not use otherwise.
Large Samples – t can be used even for clearly
skewed distributions
#63
HOMEWORK #2

Pg 518 (63, 67-70, 72-78)