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 Post subject: Telephone number and digitsPosted: Sat Dec 23, 2017 7:22 pm

Joined: Sat Jan 09, 2016 6:45 pm
Posts: 303
Can anyone help with the following?

The last part of a telephone number has four digits eg

7814 1487 2103 2772

The last part of the telephone number can start with any digit apart from zero. The other three digits can be any number. How many four digit numbers are there?

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 Post subject: Re: Telephone number and digitsPosted: Sat Dec 23, 2017 7:35 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
X X X X

How many digits can go in place 1? Place 2? .... so how many options altogether?

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 Post subject: Re: Telephone number and digitsPosted: Sun Dec 24, 2017 6:09 pm

Joined: Sat Jan 09, 2016 6:45 pm
Posts: 303
Thanks! DD had put 9000 so I wanted to try and work out if she was correct

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 Post subject: Re: Telephone number and digitsPosted: Wed Dec 27, 2017 3:45 pm

Joined: Fri Mar 10, 2017 5:06 pm
Posts: 682
Yes I think your DD is correct.

The way I would think of it is, if there were no restrictions on any of the digits the number of possibilities would obviously be 10,000. (0000 - 9999).

But you are not allowed 0000 - 0999 so you have to subtract these 1000 numbers leaving 9000.

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