23 January 2011

How to validate a credit card number with your head using a checksum as presented on mint.com's blog. Take the above number (or any credit card number). And double every other digit from the right. Add these new digits to undoubled ones. All double digit numbers are added as a sum of their digits, so 14 becomes 1+4. If the final sum is divisible by 10, the number is invalid or fake. Try it and see.

How to validate a credit card number (click for full pic)

[via:Viralliset Linkit]

25 October 2009

Math Overflow, a Questions and Answers site for math problems

Implemented using the platform of Stack Overflow, a Q&A board for programming topics. Beats any old-type forums or wiki sites, they have among other things, an addicting reputation and badge system inspired by Xbox Live.

[via:Spolsky]

23 October 2009

1. A 3-kg object is released from rest at a height of 5m on a curved, frictionless ramp. At the foot of the ram is a spring of force constant k = 100 N/m. The object slides down the ramp and into the spring, compressing it a distance x before coming to rest. (a) Find x (b) Does the object continue to move after it comes to rest? If yes, how high will it go up the slope before it comes to rest U =  3(9,21)(5)=147,15 U5 = 1/2(100x^2 = 50x^2 ...? NO. There is an elephant in the way
Not only is there an elephant, but it’s levitating.

[via:rands]

15 August 2009

“When Zombies Attack!: Mathematical Modelling of an Outbreak of Zombie Infection,” by Philip Munz, Ioan Hudea, Joe Imad and Robert J, Smith.

In “Infectious Disease Modelling Research Progress,” eds. J.M. Tchuenche and C. Chiyaka, Nova Science Publishers, Inc. pp. 133-150, 2009.

Wired provides a summary.

[via:Slashdot]

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