This is the fourth part of the Math and Multimedia’s Math Tricks and Shortcuts Series. In this post, I am going to discuss a shortcut on multiplying numbers by 13 (my aplogies to all the triskaidekaphobic). Well, I am not really sure if you would like to call it a shortcut since multiplying large numbers by 13 using the conventional method might be faster. Anyway, I am going to show you though that it works with few cases and we will later discuss why it works.
Shortcut on Multiplying Numbers by 13
Append 0 before and after the number you are multiplying by 13.
Starting with the ones digit of the original number, multiply it by 3 and add the product to the next digit on the right. The result of this calculation is the ones digit of the product of the number and 13.
Do the process again to the tens digit. Multiply it by 3 and add the product to the next digit on the right. The result of the calculation is the tens digit of the product of the number and 13. » Read more
This is the third part of the Math and Multimedia Math Trick Series. The first two tricks are multiplying by 11 and squaring numbers ending in 5.
As I have promised, I will teach you more math tricks that will impress your friends. The most exciting part, however, is not actually the trick but why the trick works. In this post, we are going to learn math trick which we will call magic 1089, a trick I learned at BasicMathematics.com.
The 1089 Math Trick
Step 1: Think of a 3-digit number where its digits are decreasing.
Step 2: Reverse the order of the digits.
Step 3: Subtract the number in step 2 from the number in step 1.
Step 4: Reverse the order of the difference in step 3.
Step 5: Add the numbers in step 3 and step 4.
The result is 1089. » Read more
In the previous post, we learned a cool math trick on squaring numbers (positive integers) ending in 5. We did not only learn the math trick itself, but we also discussed why it works. In this post, we will explore another math trick which is multiplying 2 digit numbers by 11.
The Copy-Add-Copy Method
To multiply 2 digit numbers by 11, we will use the copy-add-copy method. We will copy and add the digits of the number multiplied by 11. Below are the steps of this method.
Steps in Multiplying 2-Digit Numbers by 11
- Copy the ones digit of the number multiplied by 11 to the ones digit of the product.
- Add the ones digit and the tens digit of the number and copy the sum (see *) to the tens digit of the product.
- Copy the tens digit of the number (see **) to the hundreds digit of the product. » Read more