# Solve Simple Equations (+ or -)

In this worksheet, students solve simple one-stage equations. Key stage:  KS 3

Curriculum topic:   Algebra

Curriculum subtopic:   Solve Linear Equations (One Variable)

Difficulty level:   ### QUESTION 1 of 10

When we solve algebraic equations, our aim is to end up with one letter on one side of the equals sign and one number on the other. This is the solution.

It doesn't matter if you end up with the letter on the left or the right, it means the same thing. (a = 6 is exactly the same as 6 = a)

We do this by using inverse operations to undo things that get in the way, but remember that we must do the same thing to both sides.

Example

Solve for a

5 - a = 10

5 - a + a = 10 + a

Simplify

5 = 10 + a

Subtract 10 from both sides.

5 -10 = 10 - 10 + a

Simplify

-5 = a

a = -5

Solve for a:

5 + a = 15

a = 10

10

a = 20

Solve for a:

a - 3 = 15

a = 12

a = 5

a = 18

Solve for a:

a + 7 = 21

a = 14

a = 3

a = 28

Solve for a:

18 + a = 21

a = 14

a = 3

a = 39

Solve for a:

a - 18 = 21

a = 14

a = 3

a = 39

Solve for a:

18 - a = 21

a = -3

a = 3

a = 39

Solve for a:

a + 21 = 18

a = -3

a = 3

a = 39

Solve for a:

15 + a = 3

a = -5

a = -12

a = 12

Solve for a:

15 - a = 3

a = -5

a = -12

a = 12

Solve for a:

15 - a = -3

a = 18

a = -18

a = -12

• Question 1

Solve for a:

5 + a = 15

a = 10
EDDIE SAYS
If we subtract 5 from each side, we are left with a = 10.

5 + a = 15
5 + a - 5 = 15 - 5
a = 10

• Question 2

Solve for a:

a - 3 = 15

a = 18
EDDIE SAYS
If we add 3 to each side, we are left with a = 18.

a - 3 + 3 = 15 + 3

a = 18

• Question 3

Solve for a:

a + 7 = 21

a = 14
EDDIE SAYS
If we subtract 7 from each side, we are left with a = 14.

a + 7 - 7 = 21 - 7

a = 14

• Question 4

Solve for a:

18 + a = 21

a = 3
EDDIE SAYS
If we subtract 18 from each side, we are left with a = 3

18 + a - 18 = 21 - 18

a = 3

• Question 5

Solve for a:

a - 18 = 21

a = 39
EDDIE SAYS
Here, we need to add 18 to each side. This means we are left with a = 39

a - 18 +18 = 21 + 18

a = 39

• Question 6

Solve for a:

18 - a = 21

a = -3
EDDIE SAYS
This one is a bit more complicated. We firstly don't want to have the a as a negative so we add it to both sides. Then we must subtract 21 from each side to simplify the equation, so a = -3

18 - a + a = 21 + a

18 = 21 + a

18 - 21 = 21 + a -21

-3 = a

• Question 7

Solve for a:

a + 21 = 18

a = -3
EDDIE SAYS
If we subtract 21 from each side, we are left with a = -3

a + 21 - 21 = 18 - 21

a = -3

• Question 8

Solve for a:

15 + a = 3

a = -12
EDDIE SAYS
If we subtract 15 from each side, we are left with a = -12

15 + a - 15 = 3 - 15

a = -12

• Question 9

Solve for a:

15 - a = 3

a = 12
EDDIE SAYS
Once again, we have a negative for our unknown so our first step is to add a to both sides to make it positive. If we then subtract 3 from both sides, we are left with a = 12

15 - a + a = 3 + a

15 = 3 + a

15 - 3 = 3 + a - 3

12 = a

• Question 10

Solve for a:

15 - a = -3

a = 18
EDDIE SAYS
Once again, we have a negative for our unknown so our first step is to add a to both sides to make it positive. If we then add 3 from both sides, we are left with a = 18

15 - a + a = -3 + a

15 = -3 + a

15 + 3 = -3 + a + 3

18 = a

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