Welcome to Windows 7 Forums. Our forum is dedicated to helping you find support and solutions for any problems regarding your Windows 7 PC be it Dell, HP, Acer, Asus or a custom build. We also provide an extensive Windows 7 tutorial section that covers a wide range of tips and tricks.

# Windows 7: Today's Puzzle

 19 May 2013 #61 Kari Windows 10 Pro x64 EN-GB 17,861 posts A Finnish ex-pat in Leipzig, Germany Correct, John. That was too easy :). X = 2 + ½X = 4 3 * 4 = 12 My System Specs
 19 May 2013 #62 sk0t0s Windows 10 Pro 64-Bit 2,073 posts Jeddah, Saudi Arabia 7 and a half kilos? My System Specs
 19 May 2013 #63 sk0t0s Windows 10 Pro 64-Bit 2,073 posts Jeddah, Saudi Arabia Quote: Originally Posted by Kari Correct, John. That was too easy :). X = 2 + ½X = 4 3 * 4 = 12 I thought it was a trick question... My System Specs
 .
 19 May 2013 #64 Kari Windows 10 Pro x64 EN-GB 17,861 posts A Finnish ex-pat in Leipzig, Germany NExt one, a bit more difficult but still doable. As this is widely used in teaching statistics and probabilities, the answer can be easily found around the interwebs but try to figure this out by yourself before searching the answer. A group of people. How big must the group be to be absolutely 100% sure at least two persons in the group have the same birthday, are born on the same day and month for instance one in April 14th 1970 and another the same April 14th 1967? How big must the group be that probability to find two people with same birthday is 99%? How big must the group be that probability to find two people with same birthday is 50%? My System Specs
 19 May 2013 #65 tom982 Windows 8.1 Pro x64 2,587 posts England Quote: Originally Posted by Kari NExt one, a bit more difficult but still doable. As this is widely used in teaching statistics and probabilities, the answer can be easily found around the interwebs but try to figure this out by yourself before searching the answer. A group of people. How big must the group be to be absolutely 100% sure at least two persons in the group have the same birthday, are born on the same day and month for instance one in April 14th 1970 and another the same April 14th 1967? How big must the group be that probability to find two people with same birthday is 99%? How big must the group be that probability to find two people with same birthday is 50%? I know it's 23 people for 50% and I seem to recall that 99% is achieved at around the 50 mark but my calculator can't handle calculations larger than 365^39 so I haven't got a hope in hell of working that one out! My System Specs
 19 May 2013 #66 mitchell65 Microsoft Windows 7 Home Premium 64-bit 7601 Multiprocessor Free Service Pack 1 5,591 posts Cornwall UK Well it's got to be 367 for 100% certainty (in a leap year) The other two I will have a go at later after taking my dog for a walk (Never know might meet Carl) My System Specs
 19 May 2013 #67 Kari Windows 10 Pro x64 EN-GB 17,861 posts A Finnish ex-pat in Leipzig, Germany Correct, Tom and John. In probability theory this is known as the Birthday problem. Due leap years, 100% probability needs 367 people, but surprisingly the 99% probability only needs 57 people, and 50% probability only 23 people. It is an interesting example of probability theory, how statistics work. My System Specs
 19 May 2013 #68 tom982 Windows 8.1 Pro x64 2,587 posts England Quote: Originally Posted by Kari Correct, Tom and John. In probability theory this is known as the Birthday problem. Due leap years, 100% probability needs 367 people, but surprisingly the 99% probability only needs 57 people, and 50% probability only 23 people. It is an interesting example of probability theory, how statistics work. For those of you who remember the Flame malware that came to light last year, this is the main theory behing the MD5 collision attack that gave Flame a, what seemed to be, legitimate digital signature: http://www.trailofbits.com/resources/flame-md5.pdf My System Specs
 19 May 2013 #69 Kari Windows 10 Pro x64 EN-GB 17,861 posts A Finnish ex-pat in Leipzig, Germany Quote: Originally Posted by tom982    Quote: Originally Posted by Kari Correct, Tom and John. In probability theory this is known as the Birthday problem. Due leap years, 100% probability needs 367 people, but surprisingly the 99% probability only needs 57 people, and 50% probability only 23 people. It is an interesting example of probability theory, how statistics work. For those of you who remember the Flame malware that came to light last year, this is the main theory behing the MD5 collision attack that gave Flame a, what seemed to be, legitimate digital signature: http://www.trailofbits.com/resources/flame-md5.pdf This is also an interesting read: Birthday attack - Wikipedia, the free encyclopedia My System Specs
 19 May 2013 #70 Britton30 Windows 7 Ultimate X64 SP1 24,343 posts Mt. Crumpit/Whoville I'm still trying to figure out the bricks. My System Specs