Question

Could someone go over with me on this question and see if my idea on doing it is right?

Answer 1

A manufacturer of paper used for packaging requires a minimum strength of 1400 g/cm2. To check on the quality of the paper, a random sample of 10 pieces of paper is selected each hour from the previous hour’s production and a strength measurement is recorded for each. The standard deviation σ of the strength measurements, computed by pooling the sum of squares of deviations of many samples, is known to equal 140 g/cm2, and the strength measurements are normally distributed.

(a) What is the approximate sampling distribution of the sample mean of n = 10 test pieces of paper?
(b) If the mean of the population of strength measurements is 1450 g/cm2, what is the approximate probability that, for a random sample of n = 10 test pieces of paper, x < 1400?
(c) What value would you select for the mean paper strength μ in order that P(x< 1400) be equal to 0.001?

Answer 2

So for a, would I just use the z score formula and get the proportion that way? would I just use the z-score formula for each question and just find the z-score values

Answer 3

a sampling of 10 would be a small sample, so you would be using the t-table

Answer 4

ummm t-table???

Answer 5

a large sample is greater than or equal to 30 and uses the z-table, z-score, etc. a small sample is less than 30 and uses the t-table, t-score

Answer 6

oh.....umm so is there a formula to find the t-score.

Answer 7

m guessing its like the z-score

Answer 8

im*

Answer 9

also, could i check with u if i used the correct table to use for a certain question?

Answer 10

sorry, it's the same formula for both z and t scores, i don't know why i brought that up
t = (x - mean)/s.d.

Answer 11

oh, sorry. I'm just trying to find that in my notes bc i don't remember going over it. Maybe i passed it over.

Answer 12

In a certain population, 15% of the people have Rh-negative blood. A blood bank serving this
population receives 92 blood donors on a particular day.
(a) What is the probability that 10 or fewer are Rh-negative?
(b) What is the probability that 15 to 20 (inclusive) of the donors are Rh-negative?

Answer 13

for that question i used binomial normal distribution

Answer 14

is that the correct thing to do

Answer 15

wait..don't i only use the t table when the standard deviation is not known?