Adoctor wants to estimate the mean hdl cholesterol of all 20 to 29 year old females. how many subjects are needed to estimate the mean hdl cholesterol within 2 points with 99% confidence assuming s = 11.1 based on earlier studies? suppose the doctor would be content with 95% confidence. how does the decrease in confidence affect the sample size?

99% requires subjects

95% requires subjects

how does the decrease in confidence affect the sample size?

99% confidence requires 243 subjects

95% confidence requires 118 subjects

The decrease in confidence makes the sample size smaller.

Step-by-step explanation:

The sample size n in Simple Random Sampling is given by

where  

z = 2.807 is the critical value for a 99% confidence level (*)

s = 11.1 is the estimated population standard deviation

e = 2 points is the margin of error

so  

(*)This is a point z such that the area under the Normal curve N(0,1) outside the interval [-z, z] equals 1% = 0.001

It can be obtained in Excel with

=NORMINV(1-0.0025,0,1)

and in OpenOffice Calc with

=NORMINV(1-0.0025;0;1)

A 95% confidence level would only change the value of z, which now would be 1.96, and the sample size changes to

The decrease in confidence makes the sample size smaller.

let x be the money she spent so that she can earn the free t-shirt.

since, she already spent $112.49

⇒

also, as per the statement: jennifer must spend $250 or more in order to qualify for a free t-shirt at the store.

then,

we have an inequality i.,e

subtract 112.49 from both sides we get;

therefore, $137. 51 more money does jennifer need to spend so that she can earn the free t-shirt