Question

How many 7 digit phone numbers are possible if the first digit cannot be zero or one and the last digit must be seven? Write your answer in scientific notation.

Answer 1

To find the number of ways to write the 7 digit phone number if the first digit cannot be zero or one and the last digit must be seven:

So,

For the first digit, there are 8 possible numbers from 2 to 9.

For the second digit, there are 10 possible numbers from 0 to 9.

For the third digit, there are 10 possible numbers from 0 to 9.

For the fourth digit, there are 10 possible numbers from 0 to 9.

For the fifth digit, there are 10 possible numbers from 0 to 9.

For the sixth digit, there are 10 possible numbers from 0 to 9.

For the seventh digit, there is only 1 possible number 7.

Hence,

`8*10*10*10*10*10*1=8*10^5`

Hence, the number of possible ways are,

`8*10^5`