Wang's Mental Math Theory

How do they do it?
Every time parents see a child to perform Mental Math and answer faster than adults using calculators, they always ask, “How can a child do that?” The key to Mental Math is the order in which digits in a problem are added or subtracted. Conventional math does calculations from right to left. My mental math method does calculations from left to right.

For example, let's add 346 and 251. The conventional way to add 346 and 251 is to start by adding the digits in the ones place. In other words, conventional math performs the calculations from right to left.

Our Mental Math method performs calculations in the opposite direction, from left to right. To add 346 and 251, we first add the digits in the hundreds place. When you compare the two methods, you can see that you cannot begin to add the two numbers by the conventional method until after you have finished reading both numbers. In the Mental Math method, you start to add the numbers as soon as you read the first digit of the second number. When you have finished reading the second number (the time you begin adding in the conventional method), you have finished the addition. Adding or subtracting from left to right is faster than from right to left.

You may wonder if the Mental Math method works on problems where you must carry over (addition) or borrow (subtraction). We will answer that question in the next section; the complete answer and methods to handle carrying over and borrowing are found in “Explore the Secrets of Mental Math,” Levels 3-6.

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