Calculating Base 10 Logarithms in Your Head

Posted 7.9 years ago.

Calculating base 10 logarithms in your head on the fly is a lot easier than you may think. It is sim...

Checking a Number for Primeness

Posted 7.9 years ago.

The Pen-and-Paperless version!
The following is roughly my thought processes when I try to check to ...

Divisibility Rules for Arbitrary Divisors

Posted 7.9 years ago.

It's rather obvious when a number is divisible by 2 or 5, and some of you probably know how to tell ...

Counting Terminating Zeros in a Factorial

Posted 7.9 years ago.

Ever notice how large factorials always end in a ton of zeros? If not, take a look at 999 Factorial ...

Converting Repeating Decimals Into Fractions

Posted 7.9 years ago.

It's fairly easy to take a fraction and turn it into a repeating decimal by hand. This is simple div...