How To Be a Human Calculator

Have you ever wanted to be able to calculate large mathematical problems faster than a calculator? Think it's not possible? Think again. Many people are catching on to the easy math methods that make them human calculators and you can too. Here's how to multiply two 2-digit numbers in your head in about 5 seconds.

Step 1

Think of your base number. Before you start to calculate your answer, you need to consider how close your two numbers are to a certain base. So, for example, if your two numbers you needed to multiply in your head are 98 and 97, the closest base number would be 100. You must know your base number before you can be a human calculator and solve this question.

Step 2

Consider how close your two numbers are to your base number. Now that you know your base number, calculate how far away your two numbers are from your base number.

You will find that 98 is -2 away from 100, and 97 is -3 away from 100. Those two numbers (-2 and -3) are very important, so write them down above each number (with the -2 above the 98, and the -3 above the 97).

Step 3

Cross-subtract. This is a technique that you've probably never seen before, but it's going to wow your friends and make them truly believe that you are a human calculator. What you need to do is cross-subtract. By that, I mean you must take your first number (98) and the distance your second number is away from your base (-3) and subtract the two. (If you want to get technical, we're actually adding the two, but to keep the terms straight in your mind, let's just call it subtraction). So if you do this, you'll get 98 - 3 = 95. (You'll find that cross-subtracting with your other numbers works too, since 97 - 2 = 95 as well.) Hang on to that number 95, as it's the first two digits of your answer. (Yes, we're already half-way done solving this mathematical problem!)

Step 4

Multiply your two floating numbers. Now you need to look at the two numbers you wrote above 98 and 97, which are -2 and -3. You need to multiply those two numbers together. So, if you are familiar with multiplication, you should know that a negative times a negative will leave you with a positive number. So -2 x -3 = +6 or just simply, 6. Good. hang on to that number too. It's the last digit in your answer.

Step 5

Look at your base to determine how to write your last two digits. You'll need to look back at your base one final time to see how many digits there are and then subtract one digit spot. So for example, if your base is 100 which has 3 digit spots and you subtract 1 digit spot, you have two placeholders or digit spots that need to be filled with your final number that you calculated.

Take the +6 that you just calculated (-2 x -3) and consider that it needs to take up two spots or placeholders. What do you do? Simply add a ‘0' in front of it, to make the number 06. Easy as pie, right? Now you've got all the numbers you need, and you're quickly going to be able to prove your skills as a human calculator.

Step 6

Put your answer together. Now that you've solved both questions (cross-subtraction and multiplication), you can find your answer. Take the 95 and the 06 and put them together to make the number 9506. That's the answer to the mathematical question 98 x 97. Try this technique with other 2-digit numbers to see if you can convince friends and family that you are a human calculator.


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