My thoughts and experiences in Delft.
It's just life, so don't worry.
It's just life, so don't worry.
Oh woeful number 7
Posted 051911 at 05:21 PM by diced
It all started with this post
3 digits, gives 10*10*10 = 1000 numbers,
but e.g. 007, is not really a number, so are all numbers upto 099, including 000, so 100 in total
so that leaves 900 3 digit numbers in total.
Then came seven (good movie btw)
7 can be at each one of those three places. for the first one:
generates 1*10*10 options > 100
then second and third place generate:
9*1*10 (combinations starting with 0 don't count) >90
9*9*1 (again the zero's) > 81
so there are 100+90+81 = 271 possible 3 digit numbers with at least one 7 in it.
Wow, that narrowed it down more than I thougt
Why did I mention 624?
Here's what I did wrong:
I did 9*9*9 (numbers without any seven)  100 (numbers with leading zero's)  5 ( already mentioned numbers) = 624.
So actually 629 (3 digit numbers without 7, or leading 0's) is the number of dismissed numbers.
And 666 can also be dismissed (it was guessed, but not my number) Other guesses had a 7 in them, so they were dismissed already.
so 630 numbers are to be dismissed, from a total of 900, leaving 270 possible numbers.
I should have practised Combinatorics a bit more.
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3 digits, gives 10*10*10 = 1000 numbers,
but e.g. 007, is not really a number, so are all numbers upto 099, including 000, so 100 in total
so that leaves 900 3 digit numbers in total.
Then came seven (good movie btw)
7 can be at each one of those three places. for the first one:
generates 1*10*10 options > 100
then second and third place generate:
9*1*10 (combinations starting with 0 don't count) >90
9*9*1 (again the zero's) > 81
so there are 100+90+81 = 271 possible 3 digit numbers with at least one 7 in it.
Wow, that narrowed it down more than I thougt
Why did I mention 624?
Here's what I did wrong:
I did 9*9*9 (numbers without any seven)  100 (numbers with leading zero's)  5 ( already mentioned numbers) = 624.
So actually 629 (3 digit numbers without 7, or leading 0's) is the number of dismissed numbers.
And 666 can also be dismissed (it was guessed, but not my number) Other guesses had a 7 in them, so they were dismissed already.
so 630 numbers are to be dismissed, from a total of 900, leaving 270 possible numbers.
I should have practised Combinatorics a bit more.
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Comments

Posted 051911 at 05:27 PM by diced 
Meohmy, this really says a lot about you Diced! LOL
It says you have more free time on your hands than I do.... AND IM JEALOUS!!!
I would totally be spending time figuring things like that out and sharing it on my blog too if I didn't have kids screaming for attention all the time.
Numbers are my passion! :DPosted 061011 at 06:57 PM by Blueranne
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