TEKS & Objectives

7.3 Number and operations. The student applies mathematical process standards to add, subtract, multiply, and divide while solving problems and justifying solutions. The student is expected to:

7.3.A add, subtract, multiply, and divide rational numbers fluently; and

7.3.B apply and extend previous understandings of operations to solve problems using addition, subtraction, multiplication, and division of rational numbers.

We will strengthen our number sense.

I will add and subtract positive and negative integers using a number line.

1. Complete warmup.

2. Add and subtract on a number line.

To add on a number line, you just count!
Note: you can write the + if you want to, but you don’t have to. If a number doesn’t have a positive (+) or negative (-) sign in front of it, it’s assumed to be positive (+)

This example is 1 – 3.
You start on the first number in the problem, which is 1.
Then count backwards three spaces.
You land on -2, so 1 – 3 = -2.
Why do we count backwards? Because when you subtract, you take away, and the left side of the number line (<–) has smaller numbers.
Let’s look at an addition problem.

This example is -5 + 2.
You start on the first number in the problem, which is -5.
Then count forward two spaces.
You land on -3, so -5 + 2 = -3.
Why do we count forward? Because we’re adding a positive number, and positive numbers are forward, or to the right (–>).
Let’s see another one:

We start on the first number in the problem, which is -6.
Because we’re adding a positive number, we count forward 8 from -6.
This brings us to 2.
Let’s try subtracting again: -4 – 2

Remember, to subtract, you start with the first number in your problem and move backwards (<–).
Why go backwards? Because when you subtract, you take away, and the left side of the number line (<–) has smaller numbers.
This example is -4 – 2.
We start on the first number in the problem, which is -4.
Next, we count 2, going backwards.
Let’s look at some more examples: