January 2026 Edexcel IAL Decision Mathematics D1 Exam Analysis
The January 2026 Decision Mathematics D1 paper presented a well-balanced yet rigorous assessment of the syllabus. With a total of 75 marks spread across seven structured questions, it tested students' abilities in procedural precision, mathematical modeling, and logical reasoning. Overall, the paper sits at a solid medium-hard difficulty level (4 out of 5 stars), primarily due to a highly demanding linear programming integer-grid question and a complex scheduling challenge.
Where the Marks Are Won and Lost
A significant portion of the marks is concentrated in Linear Programming and Critical Path Analysis (CPA). In Question 5, students had to locate and shade a feasible region defined by three constraints, but the real differentiator was part (d). Finding the optimal integer coordinates near the fractional vertex \( C \) required a rigorous examination of the surrounding integer grid points. Many students lost several of the 7 marks here by failing to show structured testing or by simply guessing. In CPA (Question 6), while finding early and late event times is typically straightforward, constructing a successful scheduling diagram with exactly three workers and a tight 22-hour deadline tested students' deep conceptual understanding of floats and resource limits.
Key Examiner Pitfalls to Avoid
- Rounding Penalties in Sorting & Bin Packing: In Question 1, several candidates wrote values like "5" instead of "5.0", losing the final Correct Solution Only (CSO) mark. Always maintain the precision of the original data list.
- Incorrect Pivot Selection: In the Quick Sort, you must select the pivot strictly according to the specified rule (middle-left or middle-right). Choosing a random element or failing to list pivots clearly leads to immediate loss of accuracy marks.
- Dijkstra's Order of Labelling: In Question 3, examiners strictly check that the order of labelling is strictly increasing. Any deviation or out-of-order listing in the working boxes is penalized.
- Activity-on-Node Confusion: In Question 4, drawing an activity-on-node diagram instead of an activity-on-arc diagram results in 0 marks. Dummies must be drawn with correct arrow directions to preserve precedence.
High-Yield Revision Strategy
To maximize your study ROI, prioritize mastering Linear Programming Formulations with integer coefficients, as seen in Question 7. Translating word problems into simplified, integer-coefficient inequalities (e.g., transforming percentage constraints) is a highly repeatable skill that examiners love to test. Additionally, practicing the Route Inspection Algorithm with vertex-removal variations (Question 3d) is vital. When a vertex is removed, the remaining odd nodes change, requiring a fresh pairing analysis.
Predictions for the Next Exam Cycle
Since the Simplex method did not appear in this paper, it is highly overdue for the next exam series. Make sure you are comfortable setting up Simplex tableaus and performing iterations, including interpreting final tableaus. We also anticipate a more traditional network flow or matching problem to reappear.