So, let’s say you are multiplying 568 x 100: Just count the zeros and move the decimal point that many places - to the right if you’re multiplying, to the left if you’re dividing. If you can count, you can multiply or divide by powers of 10 in your head. Multiplying or dividing something by 10, 100, or 1000 is where a lot of this begins. You can really impress people, maybe even get a date. And even on tests where calculators are allowed, doing it mentally is, again, often easier and faster once you get the hang of it.

They’re written so that the arithmetic involved isn’t too difficult, but it’s still helpful to be able to quickly calculate 15 x 20 in your head rather than writing longhand. Plenty of tests are no-calculators-allowed, in whole or in part. If I need to calculate something like sales tax or a tip, it’s usually faster and easier to do it in my head than it is to pull out my cell phone.įrom the perspective of a student, it is helpful in lots of ways. But it turns out that being able to do math in my head is actually super useful. Well, the math teachers of yore were completely wrong about me not always having a calculator in my pocket. People of a certain age (ask your parents, they’ll confirm) will remember a time when, if students complained about “no calculators allowed” math tests, the teacher would say that “you won’t always have a calculator in your pocket, you need to be able to do without.”

Mental math calculator