An unknown number is a term used in mathematics to describe an equation that has two equal sides that have a missing value either immediately before or immediately after an ‘=’. The missing value is usually defined by a letter (e.g., ‘x’) or an empty (_____) space in addition to the given values to be added together.
For example,
1) x + 5 = 8
2) 12 – ___ = 7
3) 3 × y = 15
4) 20 ÷ x = 4
The format of the unknown number can also be displayed as a general form of an equation.
Equations are comprised of three components:
1. A Left Side (also known as an expression)
2. An Equal Sign (=)
3. A Right Side (also known as an expression)
Example:
x + 3 = 10
In this instance, x + 3 is located on the Left Side of the equation and 10 is located on the Right Side of the equation. Therefore, we will need to solve for x to achieve the same value on both sides of the equation.
Solving Basic Algebraic Equations
1. Adding
Example: x + 4 = 7
Q: What is the value of x?
A: 3
Check: 3 + 4 = 7
2. Subtracting
Example: 9 – x = 5
Q: What is the value of x?
A: 4
Check: 9 – 4 = 5
Alternative: x – 2 = 6
A: x = 8
Check: 8 – 2 = 6
3. Multiplying
Example: x * 3 = 12
Q: What is the value of x?
A: 4
Check: 4 * 3 = 12
4. Dividing
Example: 20 ÷ x = 4
Q: What is the value of x?
A: 5
Check: 20 ÷ 5 = 4
Alternative: x^2 = 8
A: x = 16
Check: 16 = 8
Examples
Example 1:
Equation: x + 6 = 10
Solution: What do you add to 6 to get 10? That’s 4.
Complete Equation: 4 + 6 = 10
Example 2:
Equation: 8 – x = 3
Solution: What do you take away from 8 to end up with 3? That’s 5.
Complete Equation: 8 – 5 = 3
Example 3:
Equation: x + 7 = 12
Solution: What do you add to 7 to make 12? That’s 5.
Complete Equation: 5 + 7 = 12
Example 4:
Equation: x × 4 = 20
Solution: What number times 4 gives you 20? That’s 5.
Complete Equation: 5 × 4 = 20
Example 5:
Equation: 6 × x = 30
Solution: What do you multiply 6 by to get 30? That’s 5.
Complete Equation: 6 × 5 = 30
Example 6:
Equation: 18 ÷ x = 6
Solution: What number divides into 18 to give you 6? That’s 3.
Complete Equation: 18 ÷ 3 = 6
Example 7:
Equation: x ÷ 4 = 5
Solution: What number divided by 4 equals 5? That’s 20.
Complete Equation: 20 ÷ 4 = 5