Not certain where I found this but my quilt guild thought WOW easy
Ya start with whatcha want, and ya divide it by whatcha got So
So punch "20" into your calculator first. Hit the division key, then enter the number "ya got," which is 12. Press the = key The number 1.66666666 pops up. The copy machine wants a percentage so move that pesky decimal point to the right by two spots, and then you're done. in this case it would then be 166. forget about the others as this is not a suspension bridge.
Remember - ya start with whatcha want You begin with your GOAL. So you can enlarge or reduce size this way.