Probability theory problems
1)The probability of life for any one given star in the known universe is 5.0x10^-14 independently of life for other star. Assuming that there are 100 billion galaxies in the universe and each galaxy has 300 billion stars, what is the probability of life on at least one other star in the known universe? How does this probabiliyy change if there were only a billion galaxies, each having 10 billion stars?
2) In a class there are 4 freshamn boys, 6 freshman girls and 6 sophomore boys. How many sophomore girls must be present if sex and class are to be independent when a student is selected at random?