MYP Maths: Simultaneous Equations FAQ

MYP 4-5 students need to solve pairs of linear equations in two unknowns using substitution, elimination and graphical methods, then interpret the solution as a coordinate point. According to the IB's MYP: Mathematics guide, this sits in the Algebra strand and is assessed through Criteria A, B, C and D — not just Criterion A.

Substitution works best when one equation already isolates a variable, like y = 3x − 1. Elimination is faster when both equations are written as ax + by = c and you can add or subtract to cancel a variable. Neither method is 'more correct' — examiners accept either, provided your working is clear.

Plot both equations as straight lines on the same axes; the point where the lines cross is your solution. This method is visual but less precise by hand — examiners still expect you to read the intersection accurately and state it as an ordered pair, for example (2, 3).

Yes — in MYP 4-5 Extended mathematics, you may meet one linear and one quadratic equation solved together, usually by substitution, which produces a quadratic you then factorise or solve with the formula. Standard mathematics students in MYP 4-5 generally stick to two linear equations; the quadratic-linear leap comes fully into focus later in DP Maths.

The single most common mistake I see marking these is a sign error when subtracting equations during elimination — subtracting a negative and forgetting to flip the sign through the whole second equation. Other regulars: stopping after finding x and never solving for y, or substituting back into the wrong equation.

Turn the words into two equations first, using consistent letters for the same real quantity throughout — say a for adult tickets and c for child tickets in both equations. Solve exactly as you would any simultaneous pair, then check the answer actually makes sense in context (you can't sell −2 tickets).

Substitute both values back into the original equations, not just one — if x and y satisfy both, your answer is correct. This thirty-second check catches nearly every arithmetic slip, and it's exactly the kind of self-verification IB examiners reward under Criterion A's problem-solving descriptors.

Yes — simultaneous equations can appear in the on-screen MYP eAssessment for Mathematics, which the IB has run since 2016, as well as in school-set summative tasks. Questions typically combine a real-life context (Criterion D) with a request to solve algebraically or graphically and justify your method (Criterion C).

Simultaneous equations touch every MYP Maths criterion: Criterion A when you apply the correct method accurately, Criterion B if asked to spot a pattern across several systems, Criterion C when you explain your reasoning in words, and Criterion D when the equations model a real situation like cost, speed or age.

Most MYP schools allow a graphic display calculator (GDC) once you're comfortable solving by hand — it's genuinely useful for checking a graphical solution or handling messy decimals quickly. But examiners still want algebraic working on the page; a bare GDC answer with no method rarely earns full marks.

MYP 4-5 covers two linear equations solved by substitution, elimination or graphing. DP Mathematics: Analysis and Approaches and Applications and Interpretation extend this to three-variable systems and, at Higher Level, matrix methods. The core logic your child learns now in MYP is exactly what DP Maths builds on two years later.

Struggling with simultaneous equations alone isn't a reason to move from Extended to Standard mathematics — it's a common sticking point at exactly this stage in both pathways. Look instead at how your child copes with the wider Algebra strand overall, including functions and sequences, before making that call with their teacher.

Sit with your child while they explain out loud why they chose substitution or elimination for a given pair of equations — verbalising the method exposes gaps faster than watching them get a right or wrong answer alone. Practice built around real Criterion A-style tasks beats generic drill questions.

Targeted topical worksheets with full mark schemes build accuracy and confidence far faster than generic online quizzes. Look for practice that separates substitution, elimination and graphical methods individually, then layers in mixed real-life word problems matched to Criteria A through D for MYP 4-5.