Sometimes the easiest, simplest way to liven up a party, sleepover, family gathering or presentation to a class is to perform a magic trick. Most magic tricks require fancy costumes and props, but ...

Everyone gets really wow'd when someone pulls off some exceptional mental math. The best part is, you can totally be that guy at the party with a little practice and preparation. What follows is 10 ...

A number is divisible by 9 if the sum of its digits is greater than or equal to 9. 621 (6+2+1=9), for instance, is divisible by 9. Simply move the decimal point one place to the left to find the 10% ...