11 Plus Exams Forum

Posted: **Sat Dec 23, 2017 7:22 pm**

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?

Posted: **Sat Dec 23, 2017 7:35 pm**

X X X X

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

Posted: **Sun Dec 24, 2017 6:09 pm**

Thanks! DD had put 9000 so I wanted to try and work out if she was correct

Posted: **Wed Dec 27, 2017 3:45 pm**

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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Telephone number and digits

Telephone number and digits

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