Paper 22 Q18IGCSE 0580 May/June 2023

Question

# Question 18 Make x the subject of the formula. c = 3x/(2x-5)

This question tests your ability to rearrange a formula with fractions to make a different variable the subject. This is a crucial algebraic skill needed for solving equations and working with scientific formulae.

Step-by-Step Solution

Key Takeaway

When making x the subject of a fraction, multiply both sides by the denominator first to eliminate the fraction, then collect like terms.

Common Mistakes

Forgetting to multiply the entire left side by (2x - 5), leading to c × 2x - 5 = 3x instead of c(2x - 5) = 3x
Not factorising correctly in the final step, trying to separate 2cx - 3x without taking out the common factor x first

Exam Tip

Always check your final answer by substituting it back into the original equation with simple values to verify it works.

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