Math tricks

[Mi Tasol]

I've probably lost half my potential audience by putting the word "math" in the title of this post; nevertheless most of what's here is simple enough that even the most rabid mathophobe shouldn't be frightened.

For those who have to convert from inFerial to easy measurements

MENTALLY CONVERTING pounds to kilograms - divide by two and take away ten percent. 100lb / 2 = 50 - 5 = 45kg instead of 45.4kg - error is 0.009%

MENTALLY CONVERTING long tons to tonnes - treat as the same because one tonne is 2204pounds and the long ton is 2240lbs - error is 0.016%

MENTALLY CONVERTING short tons to tonnes - deduct 10%. One short ton is 2000 lb. 2000-200=1800lbs = 0.9 tonnes. Or 1.0 - 0.1 = 0.9 Error is 0.007%

MENTALLY CONVERTING feet to metres.
Larger measurements -Ten feet is 120 inches Three metres is 118.11 inches so calling ten feet three metres has only a 0.016% error.
For smaller foot measurements multiply by 300. One foot = 300mm, two foot = 600mm etc again has only a 0.016% error.