Hi Everyone. I received a whatsapp message today about a young Nigerian boy who has discovered a new way to test for divisibility by 7. It is called the Chika Test and here's how it works. To test if a number is divisible by 7, multiply the last digit by 5. Then add it to the remaining number. Example - 1: is 532 divisible by 7? Multiply 2 x 5= 10; Then 10+53= 63. 63 is divisible by 7 Example - 2: Is 987 divisible by 7? Multiply 7 x 5 = 35; Then 35 + 98 = 133; 133 / 7 = 19 This is one of those things that make you go "wow" Do you know of anything similar?

why is 0!=1?