Hack #38: Calculate Mental Checksums

It's often useful to know whether one number is evenly divisible by another number. Here are some tricks that go beyond knowing whether a number is odd or even, or divisible by 10.

Additions and Suggestions

Concrete ideas to modify and expand this hack go here.

Discussion

Freeform discussion of this hack goes here.

Links

• Wikipedia "Divisor" article: http://en.wikipedia.org/wiki/Divisor
• See also http://en.wikipedia.org/wiki/Divisibility_rule

Errata

Errata go here.

Hack Author

Ron Hale-Evans

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This is a page for a hack from the book MindPerformanceHacks by Ron Hale-Evans.