Classic Hacks: Quickly Multiply Big Numbers With A Visual Aid

If you're anything like me, you may have forgotten how to do many types of mathematical equations without resorting to Google or a calculator app, though having a trick up your sleeve to do so can come in handy sometimes.

This method we unearthed back in 2013 is a handy visual guide to large multiplications -- and while it may not be faster than other methods floating around out there, it's a great way for visual learners to work out multiplications that involve large numbers.

The method is demonstrated in the video above, but here's the basic gist of it: You draw diagonal lines to represent the numbers in the sum. Ie, 223 x 131 would be a group of two, two and three lines, crossed by a group of one, three and one lines. Once all the lines are drawn, you just separate the diagram into vertical slices and count up the number of intersecting lines in each slice.

While it's probably not the quickest way to get your answer, it is a method that is really easy to remember -- and I know I'll be keeping it in mind for the future. At least until we get some kind of embeddable chip that automatically calculates anything in response to a brain signal. It probably won't be long.

Lifehacker's Classic Hacks is a regular segment where we dig up the most popular, useful and offbeat advice from our archives and update it for your modern lifestyle.


    I've seen this method a few times, and every time the digits in the demo are only 1s, 2s and 3s. There's a reason for that. Try using this method to multiply 97 * 68 and see how it turns out for you.

    (And remember, you have to count every intersection by hand. Because if you use the shortcut of multiplying 9*8 to work out how many intersections there are in a cluster, you're just doing old-fashioned long multiplication and may as well skip the diagram)

    Personally the way I see it is if you need to do important maths, you'll have a calculator or the required time to go get one. I think it's an underrated skill to zequal answers. That is, to say, estimate the size of the answer instead of trying to get exact values.

    E.g., if you have to do 986,858.8 * 52,666.6, that's pretty close to 1,000,000 * 50,000, which is just 50,000,000,000. If you always round up instead of rounding down then you get an even more useful bit of information. If you did 1,000,000 * 60,000 then you can say with certainty that your number is somewhere less than 60,000,000,000. Which for "real world maths", is a perfectly fine (and totally factual) thing to say. You haven't done anything wrong mathematically, you've just made your question easier.

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