A city has to accommodate for 9.99 million households requiring a telephone number. They are about to issue 8-digit telephone numbers, with 5 as the first digit.

How many different telephone numbers can be created if repetition of digits is not allowed?

xxJenny1213xx Jan 29, 2021

#1**+1 **

181440

The First digit is 5 as said.

Each digit after that has to be different.

There are 10 digits, so we multiply 1 less each time we move to the right.

The second digit has 9 possibilities - any digit other than 5.

The third has 8 - Any except 5 and the first digit.

And so on.

So 1*9*8*7*6*5*4*3=181440

MooMooooMooM Jan 29, 2021

#1**+1 **

Best Answer

181440

The First digit is 5 as said.

Each digit after that has to be different.

There are 10 digits, so we multiply 1 less each time we move to the right.

The second digit has 9 possibilities - any digit other than 5.

The third has 8 - Any except 5 and the first digit.

And so on.

So 1*9*8*7*6*5*4*3=181440

MooMooooMooM Jan 29, 2021