Question

A random sample of representatives from seven companies were interviewed in order to find the number of computers they planned to order next year. The results are, 8,15,33,10,9,25,12.
Assuming that the population of the number of computers planned to be ordered next year is normally distributed, construct a 95% confidence interval for the population mean.

Answer 1

so first find the mean
can you do this? then i'll help with the next part

Answer 2

16.

Answer 3

right, now we need to find the standard deviation

Answer 4

the sample standard dev right?

Answer 5

exactly, do you have that equation?

Answer 6

yes i do, calculating right now

Answer 7

i got 9.45

Answer 8

nice work!

Answer 9

now do you remember the 68-95-99.7 rule?

Answer 10

cant say that i do

Answer 11

ok, so the idea is this:
68% of the sample population with be between 1 standard deviation from the mean. so in our case our mean is 16, so if I were looking for 68% of the population, then what i'm really wanting to know is what is the range that 68% of people will fall into,
I take 16+9.45 = 25.45 and do 16-9.45 = 6.65
so 68% of the population will be between 6.65 and 25.45
do you see how it works?

Answer 12

68-95-99.7 rule

68% goes with 1 standard deviation plus and minus from the mean
95% goes with 2 standard deviation plus and minus from the mean
99.7% goes with 3 standard deviation plus and minus from the mean

Answer 13

@jimkim17 you get it, ya, no? clear as mud?

Answer 14

sorry one moment, Im going with the text book at the same time, and im gonna see if it works. and ill let ya know to compare the answer.

Answer 15

in the text im using the tdistribution table
i got 16+-(2.447*3.57)

Answer 16

7.26 to 24.74