My first blog post for SchoolPage got a wonderful response. Thank you all. Based on your request for more such tricks, here is my next blog, Four multiplication tricks every student should know.
Multiplying even numbers by 5
This may not seem like a huge task when we multiply small numbers, but imagine when you have to multiply large numbers like 34569872678942 by 5. I am sure this could take some time, especially if you have to do it in your head.
Let us take a couple of examples to see how we can do this faster.
Example 1:- 100 x 5 = 500 (Yes this was a simple one and anyone can do it in their head but it will be easier to explain the shortcut with these numbers)
- The first step is to divide the number by 2. In this case we would get 100/2 = 50
- All we have to do now is add a 0 to the result and we get our answer which is 500
Example 2:- 74 x 5 = 370. Now let use the shortcut and see if we get the same number
- We divide 74/2 and get 37
- We add a 0 to the result and get 370
Go ahead try out the method with the crazy long number I gave at the beginning 34569872678942 you will get the same answer.
Multiplying odd numbers by 5
We use the same method as above to multiply odd numbers by 5 with one change. When we divide the odd number by 2 we will get a number with a decimal value. All we will have to do then is remove the decimal and we will have the answer.
Let us take an example to illustrate this further.
Example 1:- 65 x 5 = 325. Now with the shortcut method.
- First we divide 65/2 = 32.5
- We remove the decimal and have our answer which is 325
Example2:- 999 x 5 = 4995. With our shortcut method.
- We divide 999/2 = 499.5
- We remove the decimal and have our answer which is 4995
Try it out with larger numbers, it will surely make it easier when you have to multiply by 5.
Multiplying large numbers by 9
Multiplying large numbers by 9 can take some time but we can save a lot of time if we use this simple method and surely everyone will agree that we can subtract much faster than we can multiply.
The shortcut to multiply any number by 9 is to first add a 0 to the number and then to subtract original number from the result. Let us take a few examples and understand this simple method.
Example 1:- A simple example to start with to make it simple to understand the shortcut. 9 x 9 = 81
- The first step is to add a 0 to the original number. When we do this we get 90.
- Now subtract 9 from 90 and you have 81 our answer.
Example 2:- 7 X 9 = 63
- The first step is to add a 0 to 7, so that we get 70
- Now subtract 7 from 70 and we get 63 our answer.
Example 3:- A large number to make sure this method works. 7022983208 x 9 = 63206848872
- We add a 0 to 7022983208 and we get 70229832080
- We subtract the original number from our result and get 70229832080 – 7022983208 = 63206848872
Multiplying by 99
Multiplying any number by 99 can take a few steps but there is a sure and short method of getting the same result but, it will surely take less time if you are quick with your subtractions.
All one has to do when multiplying any number by 99 is to multiply it by 100 instead and then subtracting the original number from the result.
Let us take a few examples.
Example 1:- A simple one to illustrate the method. 99 x 99 = 9801
- First we multiply the number by 100 instead of 99. So we get 99 x 100 = 9900
- Now we subtract 99 from the result and we get 9900 – 99 = 9801
Example 2:- 349 x 99 = 34551
- We multiply the number by 100 instead of 99. So we get 349 x 100 = 34900
- Now we subtract 349 from the result and we get 34900 – 349 = 34551
Knowing these shortcuts can surely help save a lot of time but there is no substitute to hard work and knowledge. In order to get the maximum benefit of these shortcuts students will have to have a strong foundation of the basics.
Having a strong grasp of the multiplication tables will be essential when using these shortcuts. Most students miss or ignore learning the multiplication tables and if they do so, knowing all these shortcuts will be in vain since the simple calculations that will be needed in these shortcuts will not be possible.