Hi I have some uni problems in my exam revision i can't sort out.

m=215mg

sd=15mg

normal distribution

215mg of nicotine in a standard cigarette

a) find the probability a single cigarette has a nicotine content more than 220mg

b) if a random sample of 25 cigarettes is selected, what is the probability that the mean is more than 220mg

I tried using Z=y-u/sd but the z score from the table was 0.629 which can be correct right?

Mr F says: Obviously **NOT** since .
PLEASE help i dont know what model i should be using!!

Also, i have no idea about part b! HELP!