Some companies who make those annoying phone calls to try to sell you something gen-
erate the phone numbers randomly.
a) Given that seven-digit phone numbers NNN-
can't have a 0 or a 1 as the first digit, how many
different phone numbers are possible (within one
area code)?
b) One company is working your area code tonight,
10 people each making an average of 20 calls per
hour. If it takes your family a half hour to eat
supper, what's the probability you get a call during mealtime?