Name: james
Who are you: Other (All)

I need to know the chance of finding a specific 8 digit number in a 11 digit mobile phone number.
the number must be 29571596 and the 11 digit phone number must end in this.
All numbers 0-9 are used in a mobile number but the first 2 digits will always be 07.
Is there a way to work this out??
thank you


Hi James.

When dealing with "chances" we want to know X selected choices out of Y possible choices.

You say that you are looking for a specific sequence of 8 digits in an 11 digit mobile phone number but all mobile phone numbers start with 07, so both the possible choices and the selected choices match on the first two digits and we are left with a nine digit problem.

According to your description, there are 10 possible choices for each of those nine digits, so that is 109 "possible choices".

The selected choices are all the nine digit numbers ending in 29571596. Since the last eight digits are set, the only choices are in that leading digit. There are ten choices in each digit, so there are ten "selected choices".

"selected choices" out of "possible choices" is therefore 10 out of 109 which simplifies to 1 out of 108. Those are your chances given the information you've told me.

Stephen La Rocque.>