statistics
posted by Sue .
Boxes of bran flakes are known to be normally distributed with a mean weight of 475g and a standard deviation of 10g.Calculate the probability of a box having a weight exceeding 485 grams. Calculate the probability that the mean weight of sixteen boxes will exceed 480g.

Use zscores.
Formula for the first part:
z = (x  mean)/sd
With your data:
z = (485  475)/10
I'll let you finish the calculation.
Once you have the zscore, check a ztable for the probability. (Remember the problem is asking "weight exceeding" 485 grams.)
Formula for the second part:
z = (x  mean)/(sd/√n)
With your data:
z = (480  475)/(10/√16)
I'll let you finish the calculation.
Once you have the zscore, check a ztable for the probability. (Remember the problem is asking "mean weight... will exceed" 480 grams.)
I hope this helps and will get you started.