When the crisp-and-crude method of calculation, which yields an approximate instead of an exact answer to a problem, is done on a mask rather than on an envelope or a napkin.
With billions of people wearing a face mask to shield themselves against the coronavirus, the back-of-the-mask thinking is a lifelong guesstimation skill math teachers and tutors worldwide ought to promote to students during this pandemic crisis.
by MathPlus September 20, 2020