Mental math is an incredible tool to offer students! It will help them self-assess the work they do on calculators as they get into more complex math, assist with quick calculations so they don't have to grab a calculator, and let them run numbers when they don't have a paper or pen. This 2 page document gives the very simple rule for mental math to multiply numbers by three different groups: 1) 10, 100, 1000, etc. 2) 0.1, 0.01, 0.001, etc. 3) 1/10, 1/100, 1/1000, etc. The worksheet includes on