Maths

Division by 2 and 5

Division is seen by some people has being hard.
But it really is very simple. Like many things in maths, it looks a lot harder than it is.
One of the major problems in division is the language.
In this introduction we will look at the words that are often used and get to know what they mean.

Tests of divisiblity

....or how can we tell if a number can be divided exactly by another number?
What we are going to show you today are things you can and should use everyday to see if you can divide a number by other numbers.
In fact these rules must be used regularly to be effective.

Dividing by 2

How can we tell if a number can be divided exactly by 2?

This is easy:

if the number is an even number and is not zero (0).

Example:

The following can be divided by 2:

Which of the following can not be divided by 2?

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Answer
These numbers can not be divided by 2. They are all odd.
35     57     39     131     135     137

What do you notice about the last digit in the numbers? 
They all end in 1, 3, 5, 7, 9
All numbers that end in 1, 3, 5, 7, 9 are odd and can't be divided by 2.

Knowing both these rules helps us to know if a number can be divided exactly by 2.

A quicker way of saying ".......can be divided exactly by" is "..... is divisible by".

Example: 
Can 24567 be divided exactly by 2? 
A quicker way of asking the same question is: is 24567 divisible by 2?

The answer is easy to find if we look at the last digit.
Is the last digit odd or even?
Answer: odd (7)
So 24567 is not divisible by 2.

Here we have introduced a new word
Divisible.

Let's use this word:

All even number except 0 are divisible by 2

Do you understand this now?
I hope so! If not, quickly re-read the last section. Then come back

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Dividing by 5

Any number that ends in a 0 or a 5 is divisible by 5

Example:

That wasn't too hard was it?

To finish off, here is a table with some numbers in it. See how quickly you can go through it. Why not time yourself? I have done the first one for you.

 
Answers

Here are the answers:

Well, how did you do?
Tomorrow we will introduce rules to help you with both 3 and 9.
Good luck!

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