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
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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