A geologist has collected 10 specimens(标本/標本) of basaltic rock(玄武岩岩石) and 10 specimens of granite(花岗岩/花崗岩). The geologist instructs a laboratory assistant to randomly select 15 of the specimens for analysis.

• (a) What is the pmf of the number of granite specimens selected for analysis?
• (b) What is the probability that all specimens of one of the two types of rock are selected for analysis?
• (c) What is the probability that the number of granite specimens selected for analysis is within 1 standard deviation of its mean value?