SOLUTION: How do you solve: Mark can remember only the first 4 digits of his friend's phone number. He also knows that the number has 7 digits and that the last digit is not a 0. If Mark

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Question 372507: How do you solve:
Mark can remember only the first 4 digits of his friend's phone number. He also knows that the number has 7 digits and that the last digit is not a 0. If Mark were to dial all of the possible numbers and if it takes him 23 seconds to try each one, how long would it take to try every possibility?
Thank you very much!
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
So he needs the final three digits.
The first digit can be from 0-9.
The second digit can be from 0-9.
The third digit can be from 1-9 since he knows it's not a 0.
In total, then the numbers can be,
N=10%2A10%2A9=900numbers
If each number takes 23 seconds, then
T=900%2A23
highlight%28T=20700%29seconds.
There are 3600 seconds in 1 hour,
T=5.75 hours or 5 hours and 45 minutes.