To simplify calculations, swap the numbers:
It’s always a true fact that, for any numbers X and Y,
X% of Y = Y% of X
Practical use case:
Calculating the #waiter’s tip in a #restaurant. If the final #bill is €86. Instead of working out 10%x€86, consider 86%x€10 which is €8,60. Swapping makes it way faster & a neat trick to teach kids.
