The Power of Mental Math

Mental Math · Axiom Academy

Simple techniques turn hard-looking arithmetic into a few easy steps — often faster than reaching for a calculator. The trick behind fast mental math Mental math is not about memorizing endless tables or being a human calculator. It is about reshaping a hard-looking problem into a couple of easy steps you can do in your head. Watch one of those moves in action. Take 47 + 38 . Instead of wrestling with the 38, bump it up to a friendly 40 , add that, then take back the little bit you overshot: 47 + 40 - 2 . Same answer, far less effort. A scary-looking sum becomes three easy moves: round up, add, adjust. Drag the two sliders. Whatever numbers you pick, the same move works: round the second number to the nearest ten, add that friendly amount, then adjust by the small difference. The final answer is always exact. Sometimes you round up and take a little back; sometimes you round down and add a little on. Either way, the friendly number does the heavy lifting. Here is a second technique. To multiply any number by 5, tack a zero on the end (that multiplies by 10) and then take half — because , and halving is easy. Drag the slider and watch it work. 47 ×︎ 5 looks like work, but 470 ÷ 2 = 235 is a snap — that is the whole trick. A toolbox for everyday numbers Rounding and adjusting, and turning into , are just two moves in a whole toolbox. Every technique in this course does the same job: it trades one hard step for a couple of easy ones.

This is the written version of the interactive lesson above. See the full Mental Math course.