Question

2. At a certain university in the U.S., all phone numbers are 7-digits long and start with either 824 or 825. (a) How many different phone numbers are possible? (b) How many different phone numbers are there in which the last four digits are all different?

          2. At a certain university in the U.S., all phone numbers are 7-digits long and start with
either 824 or 825.
(a) How many different phone numbers are possible?
(b) How many different phone numbers are there in which the last four digits are
all different?

2. At a certain university in the U.S., all phone numbers are 7-digits long and start with
either 824 or 825.
(a) How many different phone numbers are possible?
(b) How many different phone numbers are there in which the last four digits are
all different?

Added by Mark P.

Calculus: Early Transcendentals

James Stewart 8th Edition

Instant Answer

Solved by Expert Steven Clarke

04/24/2022

Step 1

So, we have 10 choices for each of the last four digits, resulting in \(10^4 = 10,000\) different phone numbers possible for each starting with 824 and 825. Therefore, the total number of different phone numbers possible is \(10,000 + 10,000 = 20,000\). Show more…

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