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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?

 Jan 29, 2021

Best Answer 

 #1
avatar+536 
+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

 Jan 29, 2021
 #1
avatar+536 
+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
 #2
avatar+467 
0

thank you!!

xxJenny1213xx  Jan 29, 2021

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