MYP Maths: Sequences & Series — Assessment, Formulas & Common Mistakes

A sequence is an ordered list of numbers following a rule — like 2, 4, 6, 8. A series is what you get when you add those terms together: 2 + 4 + 6 + 8. Students mix these up constantly on Criterion A questions, so I always tell mine: sequence lists, series adds.

An arithmetic sequence adds (or subtracts) a fixed common difference between terms — 3, 7, 11, 15. A geometric sequence multiplies by a fixed common ratio — 3, 6, 12, 24. Spotting which one you've got is the first mark on almost every MYP sequences question, before you touch a single formula.

Find the common difference or ratio first, then substitute it into the correct formula — u_n = u_1 + (n − 1)d for arithmetic, or u_n = u_1 × r^(n−1) for geometric. For 5, 8, 11, 14, the difference is 3, so u_n = 5 + (n − 1) × 3 = 3n + 2.

You need four core formulas: the arithmetic nth term, the arithmetic series sum, the geometric nth term, and the geometric series sum (for r ≠ 1). MYP doesn't hand you a formula booklet the way the DP does, so by MYP 5 examiners expect these memorised, not looked up mid-test.

Sequences and series isn't graded through its own criterion — it's assessed across the four standard MYP Mathematics criteria: A (Knowing and understanding), B (Investigating patterns), C (Communicating), and D (Applying mathematics in real-life contexts). According to the IB's MYP: Mathematics guide, each criterion is marked out of a maximum of 8, and these combine into your final 1-7 grade.

Criterion B (Investigating patterns) is where sequences and series show up most heavily — tasks asking you to describe a pattern, state a general rule, then prove or verify it algebraically. Criterion D follows close behind, usually through applied contexts like compound interest, depreciation, or population growth modelled as a geometric sequence.

Yes — schools running the IB's on-screen MYP eAssessments in Mathematics regularly include sequences and series, usually as short structured items asking students to identify a pattern, state the nth term, and calculate a sum. They're marked against the same four criteria used in classwork, just under timed exam conditions.

The single biggest mistake is confusing u_1 (the first term) with u_0, which throws every following calculation off by one term. Close behind: applying the geometric sum formula when r equals 1 (it's undefined there), and stating a general rule on Criterion B without showing it holds for more than one value of n.

Practise identifying the sequence type before reaching for a formula — that habit alone fixes most lost Criterion A marks. Then focus repetition on Criterion B-style pattern tasks, since that's where students lose the most marks: stating a correct rule but never justifying why it works for every term in the sequence.

Both, and MYP tests them differently. Criterion B wants you to spot a pattern and prove your general rule holds for any term n. Criterion D wants you to apply a sequence formula to a genuine context — like calculating the value of an investment after several years using a geometric series.

Sequences and series in MYP 4-5 builds the algebraic groundwork for both DP Mathematics courses — arithmetic and geometric sequences appear directly in Analysis and Approaches, and financial applications of geometric series appear in Applications and Interpretation. According to the IB, both current DP courses were first taught in 2019 and first examined in 2021.

Yes, noticeably. MYP 1-3 sticks to simple numeric patterns and straightforward term-finding. MYP 4-5 expects algebraic generalisation, proof-style justification under Criterion B, and applied problems involving compound growth or decay under Criterion D — the jump is less about new formulas, more about being asked to prove why a rule works.

It's a useful early signal, though not the only one. A student who enjoys proving why a rule works — the Criterion B style of thinking — often suits Analysis and Approaches. One who prefers applying sequences to real contexts like finance or growth models — the Criterion D style — often leans toward Applications and Interpretation.

For MYP 4-5 sequences and series, look for topic-specific revision notes, topical worksheets with full worked solutions, and mock papers that mix Criterion B and Criterion D style questions rather than generic algebra drills. Self-study resources built around the actual MYP criteria let a student revisit exactly the skill they're weakest on, at their own pace.