Statistics students were asked to go home and fill a 1-cup measure with raisin bran and to tap the cup gently on the counter 3 times to settle the contents. Then, if necessary, add more raisin bran to bring the contents exactly up to the 1-cup line. Once at the 1-cup line, the students would spread the contents on a large plate and count the number of raisins. For the 13 students who chose Kellogg’s brand, the reported results were:23 33 44 36 29 42 31 33 61 36 34 23 24

Question

Statistics students were asked to go home and fill a 1-cup measure with raisin bran and to tap the cup gently on the counter 3 times to settle the contents. Then, if necessary, add more raisin bran to bring the contents exactly up to the 1-cup line. Once at the 1-cup line, the students would spread the contents on a large plate and count the number of raisins. For the 13 students who chose Kellogg’s brand, the reported results were:23	33	44	36	29	42	31	33	61	36	34	23	24

Assuming the population is normal, construct a 90% confidence interval for the mean number of raisins per cup.

PsyDAG · Answer

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (±.05) and its Z score.

90% = mean ± Z SEm

90% = mean ± 1.645 SEm

SEm = SD/√n

Find the mean = sum of scores/number of scores

Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.

Standard deviation = square root of variance

I'll let you do the calculations.