A numerical expression contains only numbers and operation signs. An expression with a variable contains a letter (for example x) and can take different values depending on what you substitute.
To evaluate an expression with a variable, substitute the value of the variable and carry out the operations in order.
A numerical expression has one fixed value
An expression with a variable depends on the variable’s value
Substitution turns an algebraic expression into a numerical one
Substitution into an expression
Substitute the value of the variable and evaluate.
3x+5,x=4
Substitute the variable value into the expression:
3(4)+5
=17
Choose the value of the expression.
x∗(x+1),x=5
Choose the value of the expression.
Reminder
| Type | Example |
|---|---|
| Numerical expression | 18−7⋅2 |
| Expression with a variable | 3x+5 |
| After substituting x=4 | 3⋅4+5=17 |
✅Main skill for this lesson: spot the variable, substitute a value, and evaluate carefully.