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Secondary 1 Math: Number Line and Negative Numbers


by Jimmy Ling

Secondary 1 Math is very different from primary school math. Many of the methods which are taught in primary schools are not applicable in secondary schools anymore. Many students who did well for PSLE Math struggle in Secondary Math. If you did not do well for PSLE Math, do not be demoralised. As long as you understand the concepts and put in hard work in secondary schools, you will be able to do well.

To do well in Secondary 1 Math, you must be very clear with 2 concepts. They are

1. Negative Numbers

2. Algebra

We shall cover negative numbers in this post and cover some important rules when we deal with negative numbers.

The Number Line

number line

In a number line, the numbers on the right of zero are positive while the numbers on the left of zeros are negative.

As you move to the right, the number increases. On the other hand, if you move to the left, the number decreases.

Let’s compare between 1 and 2. Which number is bigger?

Obviously, the answer is 2.

Now, let’s compare between -1 and -2. Which number is bigger?

The answer is -1. Why?

From -1 to -2, the number moves to the left on the number line and hence, it decreases. The number becomes more negative and hence, smaller.

Addition and Subtraction

Once you have understood this concept, you need to learn how to do addition and subtraction which involves negative numbers. You should have learnt this primary schools. Let’s revise again for Secondary 1 Math.

What is 5 – 8?

Let’s illustrate on a number line below.

5 minus 8

 

We shall start from 5. Minus 8 means we move 8 spaces to the left. So the number will end at -3. You can imagine -3 as shortage of 3. If you have 5 balls and you need to give 8 balls away. You will have shortage of 3 balls.

Let’s look at another one.

What is -6 + 8?

negative numbers

We start from -6 first. Plus 8 means we move 8 spaces to the right. So we will end at positive 2. However, we do not write positive 2 as +2. We simply write as 2 which is positive by default.

In fact, if you are sharp enough, you may have realised that -6 + 8 is the same as 8 – 6. Yes, you can actually move the numbers around. But remember to bring the sign along! In this case, the minus sign belongs to 6. So when you move 6 to the back, the minus sign need to follow it.

Multiplication and Division

For multiplication and division which involves negative number, you need to memorise these 4 golden rules.

1. Plus × Plus = Plus

2. Plus × Minus = Minus

3. Minus × Plus = Minus

4. Minus × Minus = Plus

A good way to memorise this is when you multiply 2 numbers of the same sign, the result is always positive.

When you multiply 2 numbers of different signs, the result is always negative.

For example,

2 × 3 = 6

-2 × 3 = -6

-3 × 4 = -12

-3 × -4 = 12

The same rules apply for division as well!

4 ÷ 2 = 2

-4 ÷ 2 = -2

4 ÷ -2 = -2

-4 ÷ -2 = 2

You must know these rules at your finger-tips before you proceed to Algebra in Secondary 1 Math. When you reach Algebra, you will need to do lots of addition, subtraction, multiplication and division which involve negative algebraic expressions.

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