A telephone number ends with a digit less than 7
asked Feb 9 in Word Problem Answers by Cyndi

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1 Answer

You haven't asked a specific question, so I don't know how long the telephone number is.

The way to find out how many numbers there are where the last digit is less than 7 is to do this multiplication:

7*10*10*...*10 for as many digits as there are or 7 followed by a number of zeroes. This number of zeroes will be 1 less than the length of the phone number, so if it's a 7-digit number we have 7000000 or 7 million numbers.

If not all the digits can be used in any other position then we multiply the number of available digits by 7 and then add the zeroes. For example, if the first digit can't be zero, then we only have 9 left to choose from so there will be 7*9=63 followed by zeroes, two fewer zeroes than the number length. For a 7-digit number there would be 6300000 possible numbers.

answered Feb 10 by Rod Top Rated User (424,740 points)
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