Primary Mathematics

How to find out if a number can be divided by 3

Many of you may wonder if a large number is given, how do you know whether it can be divided by 3. The technique is pretty simple , however, if there is no one to guide you , you would probably not aware of this technique .

Firstly, let's take a look at number 24. We all know that 24 can be divided by 3 easily as 24 is in the multiplication table. 3 X8 = 24.

If a larger number , say, 87 is given , are you able to tell if 87 can be dvided by 3 ? Yes, some of you may say it is easily done by mental caluculations.
Yes, 87 can be divided by 3 . 3X 29 = 87

Alrght, how about this number 38765865 ? Can anyone tell me if this number can be divided by 3 without going through the traditional method that thought in he prmary school ?

Well, the trick is , let's look at 24. If we add up the digit 2 and 4 , it gives you 6. And 6 is divisible by 3 , therefore, 24 can be divided by 3.

Let's look at 87 again . The sum of 8 and 7 gives you 15, some of you may know that 15 can be dividd by 3 and therefore 87 can be dividd y 3. For the sake of explaination, let me go through this. the sum of 1 and 5 gives you 6 which is divisible by 3. Therefore, 87 can be divided by 3.

Same rule applies to 38765865 , the sum of the all the dgits gives you 48, furher adition of 4 and 8 gives you 12. we add 1 and 2 again and gives you 3.
Therefore, 38765865 can be divided by 3.

By author Woei Wu

posted by Blogs @ 2:53 AM