Some of you geeks probably have a slide-rule in your head — there I go dating myself again (and we all know that dating yourself isn’t sexy), I should have said “math processor” or “calculator”. Anyway, I am personally much better than average at math, but I still can’t do some of the bigger problems in my head.
Via Mercola, I found this list of 10 Easy Arithmetic Tricks to save you the trouble of getting out a calculator for solving some math problems.
The “11 Times Trick” is one I hadn’t thought of before, but it makes perfect sense. To multiply any two-digit number by 11, you add the digits together and put the result between them, adding any excess digit to the first digit. It makes sense because multiplying it out long-hand you get (for any two digit number mn):
m n
X 1 1
———-
m n
m n
————
m(m+n)n
Some of the tricks are a bit obvious, like the multiply/divide by 5 and how to compute a 15% tip (a lot of places are starting to expect 20% now anyway). But all the tricks are good exercises for understanding how numbers work.
Here are a few more tricks that I learned somewhere along the way for determining if a decimal integer is a multiple of:
Looking at this list, the relationship between 3, 6, and 9 is obvious — as is the relationship between 4 and 8. The unique characteristics of 7 and 11 are intriguing, don’t you think?
What other arithmetic tricks do you know?
Check out this awesome video compilation of some of the best cosplays seen at Wondercon…
Ever felt the envy of that one neighbor who always has to one-up you? Well,…
Experience Star Wars like never before with Sky Elements Drone Shows' spectacular version of "A…
[Source: @jholtillus]
For today’s edition of “Deal of the Day,” here are some of the best deals…
Watch as Michael Sheen's performs Dylan Thomas' iconic poem, "Do not go gentle into that…