

Phone Number Numbers
Name: Jay
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
I recently read in this health magazine that it can be
823,542 phone numbers without the same number. According to my me
if I miscalculated? Unless the there are numbers they won't use.
Replies:
Jay,
I assume you mean a phone number, without the area code.
You are correct that there are numbers that won't be used , for example
0000000 would probably ring the operator. This deletes from availability any
of the digits beginning with 0, such as 0000000, 0000001, 0000002,
0000003.......0999999, or 1, 000, 000 combinations. You could add to this
any other 'special' numbers, such as "911" where any number beginning with
911 would not work because 911 would be contacted after the first 3 digits
were dialed. Therefore 9110000, 9110001, 9110002 ...9119999 could nto be
used. (This problem excludes 10,000 numbers.) There might be other unusable
combinations in your community which would then remove from use those
combinations. Try to identify for your community which number combinations
are not useable, and then subtract the combinations from the total possible.
If all combinations could be used the acceptable numbers would be 0000000 to
9999999. This gives 10 million combinations.
Just citing the problems I mentioned above, we have available
10,000,000 less 1,000,000 or 9 million combinations. We must also subtract
10,00 unsuitsble combinations beginning with 911.
Try this exercise for you community after checking which digits are
not used or are dedicated to special use.
Thanks for using NEWTON!
Ric Rupnik
Click here to return to the Mathematics Archives
 
Update: June 2012

