Question

HELPPP

A random sample of 145 students is chosen from a population of 4,250 students. If the mean IQ in the sample is 130 with a standard deviation of 7, what is the 90% confidence interval for the students' mean IQ score?

98.98−101.02

109−112.

125−135

129.82−130.18

Answer 1

Were you able to get started?

Answer 2

I don't fully understand what standard deviation means

Answer 3

it's the measure of spread

it tells you how dispersed the distribution is

Answer 4

a larger standard deviation means the values are more spread out and further away from the mean

Answer 5

a smaller standard deviation tells us that the values are more closely clustered near the mean

Answer 6

So where should I start?

Answer 7

you need the critical value for the 90% confidence level

Answer 8

to find that, use this table

http://3.bp.blogspot.com/_5u1UHojRiJk/TEdJJc6of2I/AAAAAAAAAIE/Ai0MW5VgIhg/s1600/t-table.jpg

Answer 9

look in the row that starts with infinity

and look in the column that corresponds to 90% confidence level

Answer 10

1.895

Answer 11

look in the bottom most row (it starts with infinity)

Answer 12

Oh okay

Answer 13

this is a t table

so it works for small samples

but for larger samples, things tend to approach the normal distribution

Answer 14

for 90,it says 1.645

Answer 15

good

Answer 16

that's the value of z

Answer 17

z = 1.645

Answer 18

now use the formula

L = xbar - z*s/sqrt(n)

to compute the lower bound of the confidence interval

Answer 19

L = lower bound
xbar = mean
z = critical value
s = standard deviation
n = sample size

Answer 20

okay

Answer 21

wait,whats the lower bound?

Answer 22

the lower bound is the left piece of the confidence interval

Answer 23

i got 6.196

Answer 24

ok let me check

Answer 25

okay

Answer 26

sorry I made a mistake, but I know how to fix it, one sec

Answer 27

okay

Answer 28

Can you help me on another question after as well

Answer 29

I'm getting close to one answer choice, but I'm off a bit in terms of the decimal portion

Answer 30

Okay,I dont mind waiting.I need the help

Answer 31

can you double check to make sure everything is typed correctly

I think there's a typo somewhere, but I'm not sure

Answer 32

Yeah its correct

Answer 33

ok, well this is what I'm getting

130 - 1.645*7/sqrt(145) = 129.043731299484

and as you can see, it's not 129.82. Not even close.

Answer 34

When I use the formula from this page

http://canmedia.mcgrawhill.ca/college/olcsupport/bowerman/2ce/OptionalContent/bow02371_OLC_7_9.pdf

see page 2

I get...

130 - (1.65*7/sqrt(145))*sqrt( (4250 - 145)/(4250) ) = 129.057329104168

a bit closer, but still not there

Answer 35

Thats the closest answer we have so I guess I will go with d

Answer 36

I also Need help on other questions if you can

Answer 37

I can do a few more

Answer 38

Sam is testing the effectiveness of a new cough medication. There are one hundred people with a cough in the study. Thirty patients received the cough medication and seventy other patients did not receive treatment. Seventeen of the patients who received the medication reported no cough at the end of the study. Twenty-eight of the patients who did not receive medication reported no cough at the end of the study. What is the probability that a patient chosen at random from this study took the medication, given that they reported no cough?

Answer 39

For problems like these, I like to set up a probability tree

Answer 40

Thirty patients (out of 100) received the cough medication, so 30/100 = 0.3 is the probability someone gets the medicine

1 - 0.3 = 0.7is the probability you don't get the medicine

Answer 41

"Seventeen of the patients who received the medication reported no cough at the end of the study"

so 17/30 = 0.567 is the approximate probability for the upper most branch

1 - 0.567 = 0.433 is for the branch below that

Answer 42

I get it so far

Answer 43

oh sry, i mixed up the two branches