The sum of the first n terms of an arithmetic series is given by Sₙ = n/2[2a + (n-1)d]. Which of the following is the correct formula for finding the sum of the first 20 terms of the series 2 + 5 + 8 + 11 + ...?

Q: How do I try a free CXC Additional Mathematics question?

Just tap any of the four options on this page — no signup, no card, nothing to install. You'll see the correct answer and a full mark-scheme-style explanation within a second. Each visit shows a fresh randomly-picked question from the live CXC CSEC Additional Mathematics bank, so you can keep refreshing to try different ones before deciding whether to create a free account for daily access.

Q: Is Kramizo really free for CXC Additional Mathematics students?

Yes — completely free. Every student gets 45 questions a day on the free plan, across any board and any subject, with no card required and no trial countdown. Kramizo's optional Pro plan removes the daily cap and adds analytics, but the free plan is genuinely free forever. We make money from the small percentage of students who choose to upgrade — not from selling data or ads.

Q: Are the Additional Mathematics questions aligned to the CXC CSEC syllabus?

Every question is written against the published CXC CSEC Additional Mathematics syllabus and reviewed for accuracy before being added to the bank. We match the command words (state, describe, explain, evaluate), mark allocations, and difficulty tier you'll see on real CXC past papers. Explanations are written in the style of official examiner mark schemes so students learn exactly what marks are being awarded for.

Question

The sum of the first n terms of an arithmetic series is given by Sₙ = n/2[2a + (n-1)d]. Which of the following is the correct formula for finding the sum of the first 20 terms of the series 2 + 5 + 8 + 11 + ...?

Accepted Answer

S₂₀ = 20/2[2(2) + (20-1)(3)] — Award 1 mark for correct substitution where a = 2, d = 3, n = 20. B is incorrect — uses n instead of (n-1). C is incorrect — omits the n/2 factor. D is incorrect — uses 2 instead of 2a in the formula.

Answer

S₂₀ = 20/2[2(2) + (20-1)(3)]

Answer

S₂₀ = 20/2[2(2) + (20)(3)]

Answer

S₂₀ = 10[2 + (19)(3)]

Answer

S₂₀ = 20[2(2) + (19)(3)]

One real Additional Mathematics question.No signup. 30 seconds.

One real Additional Mathematics question.
No signup. 30 seconds.