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ethan0
10.03.2020 •
Mathematics
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 22 seconds to try each one, how long would it take to try every possibility?
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Ответ:
19800 seconds, or 330 minutes, or 5 hours + 30 minutes
Step-by-step explanation:
Number Permutations
We know the phone number has 7 digits, 4 of which are known by Mark. This leaves him 3 digits to guess with. We also know the last one is not zero. The number can be represented as
XXY
Where X can be any digit from 0 to 9 and Y can be any digit from 1 to 9. The first two can be combined in 10x10 ways, and the last one can be of 9 ways, this gives us 10x10x9 = 900 possible permutations.
If each possible number takes him 22 seconds, every possibility will need
22x900=19800 seconds, or 330 minutes, or 5 hours + 30 minutes
Ответ:
Jane is 10 9/30 years old
Step-by-step explanation:
Given that Jeremy is 12 4 /5 years old
Carl is 1 1/6 years younger than Jeremy which is why we would subtract giving us
=12 4/5 - 1 1/6
= 11 (24- 5)/30
= 11 19/30 years
and Jane is 1 1 3 years younger than Carl which is why we would subtract giving us
=11 19/30 - 1 1/3
= 10 ( 19 - 10)/ 30
=10 9/30 years