Substituting into Formulae
Substitute numerical values into formulae and expressions including scientific formulae; evaluate expressions by replacing variables with given values and computing the result using correct order of operations
What a learner can do afterwards
- Substitute positive and negative values into algebraic expressions and evaluate
- Substitute values into formulae involving multiple operations and powers
- Use correct order of operations when evaluating expressions after substitution
The lesson
Substituting means replacing each letter in a formula with the number you are given. Write the number in place of the letter, then work out the answer.
The formula for the area of a square is A = s². To find the area when s = 4, substitute: A = 4² = 4 x 4 = 16.
When a formula has more than one operation, work out powers first, then multiplication and division, then addition and subtraction. Handle one operation at a time, in order.
The expression 3x + 7 works for any value of x. Substitute x = -4: 3 x (-4) + 7 = -12 + 7 = -5. Take care with the negative sign.
Swap each letter for its number, then follow the order of operations to find the answer.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.