Math Is Fun Forum

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

rough eighths of an inch trick

25.4 divided by 8 is within one-half
of a percent of the square-root of
ten.  This is interesting to note, in
case you are a carpenter or mechanic
with poor math skills and can't
remember if you should divide or
multiply.  Because if you start with
8th's of an inch or if you start with
millimeters, you can go either direction
by just multiplying or dividing by
the square-root of 10 on any
simple calculator.  If the answer looks
too small in one case, you hit the
wrong button and now you are in
centimeters instead of millimeters.
This is because the reciprocal of the
square-root of ten looks the same
except the decimal point is moved
over.  If you are going from millimeters
to inches and you press the wrong
multiply button instead of divide, then you
will end up close to 80ths of an inch, and
hopefully you will then either move over
the decimal place or do the problem
again by dividing instead.
I know this is very silly, but I had to
share something with you today!!!!

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igloo myrtilles fourmis

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: rough eighths of an inch trick

That is really cool fact! What is the dimension of the inch actually defined?

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: rough eighths of an inch trick

Hi John E. Franklin;

No it isn't silly. As always I liked it.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.