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Originally Posted by tagiraldo  Assume the market proportion of the phone provider XY to be 50% in a given country. Assume it means that 50% of all existing phone numbers in the country are of the provider XY.
b) What is the probability that 2 phone numbers out of 10 randomly selected are of the provider XY?
c) What is the probability that at least 2 phone numbers out of 10 randomly selected are of the provider XY? |
The number of XY's in a sample of size
has a binomial distribution
. This will give the answer to b) straight off, for part c) you will need to sum the appropriate binomial probabilities.
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d) If 100 numbers have been randomly selected, what is the probability that the we find at least 48 and less than 52 numbers that are of the provider XY?
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For this use the normal approximation to the binomial.
CB