80% phone numbers listed, 20% of the phone numbers are business; 20% start with numeral 2, 1000 # random sampl
Wednesday, February 24th, 2010 at
7:04 pm
If you were to take a random sample of 1000 phone numbers from the city’s phone book, how many numbers would be expect to be unlisted, non business phone numbers that start with a numeral other than 2?
Filed under: Business Phone Systems
80% ie 4/5 listed, so 1/5 unlisted
20 % ie 1/5 are business, so 4/5 are non business
20% ie 1/5 start with a 2 so 4/5 don’t
So…
(1/5)(4/5)(4/5)(1000) = 128
200