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. Continue reading