I know this should be easy but I'm not seeing it.
Question: On average, 3% of the watches manufactured by a particular company will be returned for warranty repair. Use the normal approximation to the binomial to find the probability that among 1000 watches sold, 40 or fewer will be returned.
I have that 3% of 1000 is 30 which is my mean.
So, (40-30)/ =probability
And I'm stuck here, because I can't see the standard deviation. Once I have that I can get a value that I can look up in the tables, correct?
Any help would be appreciated.