statistics
posted by Sandra on .
Use the normal dist to approx the desired prob. Find the prob of getting at most 30 fives in 200 tosses of a fair 6 sided die

Mean = np
SD = √npq
n = 200
p = 1/6
q = 1  p = 5/6
Therefore:
Mean = 200(1/6) = 33.33
SD = √[200(1/6)(5/6)] = 5.27
Use zscores:
z = (x  mean)/SD
z = (30  33.33)/5.27 = 0.63
Check a ztable for the probability.
(Remember the problem is asking "at most 30" when looking at the table.)