Math Is Fun Forum

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

feet to meters

Easy way to convert in head.
7 feet is what in meters?
7 x 3 = 21, so think 2.1 to start.
7 / 2 = 3.5, so think 2.135 minus a little.
7 x 2 = 14, so think 35 - 1.4 or 33.6
So 2.1336 meters is 7 feet!!!!

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igloo myrtilles fourmis

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: feet to meters

This is actually really neat to compare to the
conversion factor number and see why it works.
12 inches  x  25.4 mm = 304.8 mm in a foot = 0.3048 meters per foot conversion factor.
Now the 3048 is also 3050 - 2.
Hence
3  :  x 3
0  : do nothing
5  :  /2
-2 :  x 2 and subtract it!!!
...
Now for a harder one. You know after a while doing these you get a "feel" for where and how to line up the 3 numbers because if you mess up the alignment, it'll be wrong.
Convert 33 feet to meters.
33x3=99
33/2=165
33x2=66
Now compare 99 165 and 66 to the 7 foot example first.
7x3=21  7/2=35 7x2=14
and it went 2.135 with 35 - 1.4 for 2.1336  (maybe the 7x2=14 could be thought of as 140)
Then the 3 #'s ascend 21, 35, 140 with 2 digit right shifting when adding.
Now 33 feet...
99, 165, 660...
9.9 + .165 - .00660  (don't subtract .660 or .0660 and notice .660 > 1.65 > .0660)
So subtract 10 times less than the lower of those two or .00660
10.065 - .00660 = 10.0584 meters = 33 feet (exactly by the way, perfect conversion)
I'll keep working on it and see if I get better at it...

Last edited by John E. Franklin (2007-10-19 10:39:54)

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igloo myrtilles fourmis