Assume a country has 3-digit area codes that all have 0 or 1 as the middle digit and do not have 0 or 1 as the first digit. Use this information to answer parts (a) and (b). (a) How many area codes are possible with this arrangement? There are area codes possible. (Type a whole number.) If the country uses a 9-digit sequence for each telephone number, then how many telephone numbers does the country permit per area code? (The first two digits that follow the area code cannot be 0 or 1. Assume that there are no other restrictions.) The country's 9-digit sequence will permit telephone numbers. (Type a whole number.) (b) The country recently experienced a shortage of area codes. To avoid this, the country removed the restriction on the second digit. How many area codes are available under the new system? There are area codes possible. (Type a whole number.)
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For the second digit, we have only 1 choice (0). For the third digit, we have 10 choices (0-9). So, the total number of area codes possible is 9*1*10 = 90. For the 9-digit sequence, the first two digits cannot be 0 or 1, so we have 8 choices for each of the first Show more…
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Assume a country has 3-digit area codes that all have 0 or 1 as the middle digit and do not have 0 or 1 as the first digit. Use this information to answer parts (a) and (b). (a) How many area codes are possible with this arrangement? There are 160 area codes possible. If the country uses a 8-digit sequence for each telephone number, then how many telephone numbers does the country permit per area code? (The first two digits that follow the area code cannot be 0. Assume that there are no other restrictions.) The country's 8-digit sequence will permit telephone numbers.
Jon S.
Phone numbers in North America have 10 digits: a threedigit area code, a three-digit exchange number, and the four final digits that make each phone number unique. Neither area codes nor exchange numbers can start with 0 or $1 .$ Prior to 1994 the second digit of the area code had to be a 0 or 1 Sixteen area codes are reserved for special services (such as 911 and 411 ). In $1994,$ the last area code was used up and the rules were changed to allow the digits 2 through 9 as the middle digit in area codes. How many different phone numbers were possible after $1994 ?$
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Phone numbers in North America have 10 digits: a threedigit area code, a three-digit exchange number, and the four final digits that make each phone number unique. Neither area codes nor exchange numbers can start with 0 or $1 .$ Prior to 1994 the second digit of the area code had to be a 0 or 1 Sixteen area codes are reserved for special services (such as 911 and 411 ). In $1994,$ the last area code was used up and the rules were changed to allow the digits 2 through 9 as the middle digit in area codes. How many different area codes were possible prior to $1994 ?$
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