Who want to calculate a fraction in their head? My method for this: * Pick the lower integer square root (5) * The distance from 25 to 33 is over half the dis

Who want to calculate a fraction in their head? My method for this: * Pick the lower integer square root (5) * The distance from 25 to 33 is over half the distance from 25 to 36. * Eyeball that that little over half on a mental picture of sqrt(x) between 0 and 1. Guesstimate 0.7. * 5.7 is the guess. You can multiply that out on your head and similarly iterate on the error if you want closer.