Question

How many three-digit phone prefixes that are used to represent a particular geographic area are possible that have no 0 or 1 in the first or second digits?

Answer 1

Answer:

The number of possible three-digit phone prefixes that are used to represent a particular geographic area is 640.

Step-by-step explanation:

The phone prefixes used to represent a particular geographic area are a 3 digit code consisting of numbers from 0 to 9.

The prefix code are of the form: x x x

Condition: The first or the second place cannot take values 0 or 1.

Then the first place can be occupied by the remaining 8 digits.

Similarly the second place can also be occupied by the remaining 8 digits.

And the third place can be occupied by any of the 10 digits.

So the number of ways to construct a phone prefix for any area is:

$Possible\ number\ of\ phone\ prefixes=8\times8\times10=640$

Thus, the number of phone prefixes possible for any area is 640.