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Mar17

Adding and Subtracting Whole Numbers

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In today’s blog post we are going to look at whole numbers: what they are and how to add and subtract them.

Let’s start by understanding what whole numbers really are:

Whole numbers are numbers that aren’t a fraction or a decimal. These numbers include natural numbers (1, 2, 3…), negative numbers (-1, -2, -3…) and zero (0).

Whole numbers can be represented on the number line. On the right side of the zero, are the natural numbers and on the left side, we can find the negative numbers.

whole numbers

Adding and Subtracting Negative Numbers

In order to learn how to add or subtract whole numbers, we are going to use the number line.

  1. We need to find the first number on the number line.
  2. If we are adding, we count however many values the second number is towards the right.
  3. If we are subtracting, we count however many values the second number is towards the left.

For example: 5 –9

So, we need to locate the first number on the line.

whole numbers

If we are adding, we count however many values the second number is to the right. If we are subtracting, we count however many values the second number is to the left.

In this problem, we are subtracting, which means we need to count towards the left. The second number is 9, so we count 9 values to the left from 5.

whole numbers

So, 5 – 9 = -4

Trick:

I’m going to show you guys a small trick. I hope it helps you to add and subtract more easily.

  • If the two numbers have the same sign, we add the two numbers without paying attention to the sign, and after adding, we’ll stick the sign that the numbers had back on the final answer. For example: – 2 – 5

Both of the numbers have the same sign, so we add them: 2 + 5 = 7. Now, we just add on the sign that the two numbers had to begin with, which is the negative sign (-). The final answer, then, is -7.

  • If the two numbers have a different sign, we just subtract them: the bigger number minus the smaller number. After, we add on whichever sign the big number had onto the answer. For example: 3 – 7

Both of the numbers have different signs, so we subtract the smaller one from the bigger one: 7 – 3 = 4. Now, we just add on the sign the bigger number had: -7 (negative). Our final answer is -4.

That concludes this week’s post. If you liked this post and want to learn more elementary math, try Smartick for free.

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