Residential Telephone Numbers

In one region, 20% of all residential telephone numbers are unlisted.if five residential dwelling units are selected at random, find:
a.the probability that all residents have an unlisted number?
b. the probabilty that leat one of the numbers on the 4 is not listed.

Probability that all residents have an unlisted number?
= 0.2 * 0.2 * 0.2 * 0.2 * 0.2
= (0.2) ^ 5
= 0.00032 or 0.032%

Probabilty at least one of the 4 numbers are unlisted.
Answer: Find the probability that all numbers are listed
and subtract it from 1.00:
P (all numbers are listed) = (0.8) ^ 5 = 0.32768
1 to 0.32768 0.67232 = 67.2%

Good luck in your studies,
~ Mitch