# SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001

• Apr 23rd 2013, 06:53 PM
spacemenon
SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
Pls do share ur idea answer givn in text book is n=82 but i am getting 80 (Headbang)
• Apr 23rd 2013, 09:22 PM
chiro
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
Hey spacemenon.

What I think they mean by this question is that you need to have a value that is less than 0.001. If you choose for example 0.0009 then the answer you get for n is 81.84179 which gives an answer for n = 82 (which is in agreement with the textbook answer).

Remember that it has to be less than 0.001 which means you can't actually use 0.001 but a value that is lower and for this I choose one decimal unit down from 0.001 which is 0.0009.

I use the same technique you used just with a different critical value.
• Apr 23rd 2013, 10:11 PM
spacemenon
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
Thank you very very much for ur help :)
• Apr 24th 2013, 05:05 AM
spacemenon
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
even if u take 0.0009 instead of 0.001 still in final stage instead of 0.999 u get 0.9991 that still gives u 3.090 pls reply need to clarify this urgently
• Apr 24th 2013, 05:44 PM
chiro
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
Using R, the calculation is given as:

> (-qnorm(0.0009,0,1)*sqrt(42/5))^2
[1] 81.84179

Rounded up gives 82. The qnorm function calculates the value of x given a probability for a normal distribution with mean and standard deviation (in this case 0 and 1 respectively).
• Apr 24th 2013, 06:15 PM
spacemenon
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
Thank you for your patience ,but there are two problems here

1. i didnt find the q norm function in calculater scientific model casio fx991es we are nt allowed graphing calculaters for cambridge A LEVEL

2. They provide a normal distribution table hw can u find this answer frm the table

( i have attached the normal distribution table given to us during exam)Attachment 28127Attachment 28128
• Apr 24th 2013, 06:28 PM
chiro
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
The function I have is a function in R which is a computer software package.

The normal tables that you have do not provide enough resolution for your problem. You will either need to get more accurate tables or use a computer for this particular question (since the significance value is extremely small).
• Apr 24th 2013, 06:47 PM
spacemenon
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
i found D in my calculater can u explain in detail like the abve how to input the parameters and how did get that > sign u wrote >qnorm and i understand the qnorm is for finding the z score value just needed to knw hw to input the parameters i did D(.0009,0,1)x 2.898273 syntax error
• Apr 24th 2013, 09:08 PM
chiro
Re: SAMPLING EX4B Q6,FIND THE LEAST VALUE OF n such that p(x bar >13)<0.001
The > is just the prompt: don't worry about it.

Either you are using the wrong function or your calculator can't calculate it. The answer for the actual value should be 3.121389 in terms of your critical value for P(Z > 3.121389) = 0.0009.