Substitution

Summary and Exam Tips for Substitution

Substitution is a subtopic of Algebra, which falls under the subject Mathematics in the Cambridge IGCSE curriculum. This concept involves replacing letters with numbers to find the value of an expression. The substitution method is particularly useful for solving linear systems algebraically. The key steps include replacing the unknowns with given values and performing computations based on the correct order of operations, often remembered by the acronym BODMAS (Brackets, Orders, Division and Multiplication, Addition and Subtraction).

For example, to find the value of $3m - 5$ when $m = 6$, substitute $m$ with 6 to get $3 \times 6 - 5 = 18 - 5 = 13$. Similarly, evaluating $3x + 4y$ when $x = 10$ and $y = 2$ results in $(3 \times 10) + (4 \times 2) = 30 + 8 = 38$. Another example is evaluating $2x^2 + 3x + 8$ when $x = 4$, which gives $(2 \times 4 \times 4) + (3 \times 4) + 8 = 32 + 12 + 8 = 52$.

Practice problems often include finding the perimeter of a rectangle using the formula $P = 2(l + b)$, where $l$ is the length and $b$ is the breadth. For instance, if the length is 12 cm and the breadth is 9 cm, the perimeter is calculated by substituting these values into the formula.

Exam Tips

• Understand the Problem: Carefully read each problem to determine what is being asked before starting your calculations.
• Use BODMAS: Always apply the correct order of operations after substitution to ensure accurate results.
• Practice Regularly: Solve various practice questions to become familiar with different types of substitution problems.
• Check Your Work: After solving, review your calculations to catch any possible errors.
• Stay Organized: Write each step clearly to avoid confusion and make it easier to review your work.