What does z represent

Twelve less than a number is at most 20

According to the general equation for conditional probability if p(anb)=3/7 and p(b)=7/8 what is p(a i b)

Assume that adults have iq scores that are normally distributed with a mean of mu equals 100 and a standard deviation sigma equals 20. find the probability that a randomly selected adult has an iq between 80 and 120.assume that adults have iq scores that are normally distributed with a mean of mu equals 100 and a standard deviation sigma equals 20. find the probability that a randomly selected adult has an iq between 80 and 120.