A-LevelMathematicsSeries9709/12 · Feb/Mar 2025 · Q56 Marks

An arithmetic progression has first term 5 and common difference 6. For this progression, find the sum of all the terms that lie between 150 and 400.

An arithmetic progression has first term 5 and common difference 6. For this progression, find the sum of all the terms that lie between 150 and 400.[6]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2025). The mark or mark type is shown in brackets.

[M1] Attempt to solve either: 5+(n-1)6=150 or 5+(n-1)6=400 Attempt to determine positions of first and last terms involved.
[A1] 151/6 and 401/6 OE Can be implied by 25 or 26 and 66 or 67.
[M1] Correct use of S_n formula with their 66 and their 25
[M1] S_66 or 67 - S_25 or 26
[A1] S_66 - S_25
[A1] 11275
[M1] Attempt to find new a and l for reduced series
[A1] 155 and 395
[M1] their 395 = their 155 + (n-1)6 Attempt to find n, which results in 40, 41 or 42.
[A1] n=41 CWO
[M1] S_their 41 = (their 41)/2 (their 155 + their 395) OE
[A1] 11275

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.

Topic: Series, A-Level Mathematics (syllabus 9709). Structured question, 6 marks.
Source: A-Level Mathematics, Feb/Mar 2025 Paper 1 Variant 2, question 5.

Questions and mark schemes are from past examination papers and remain the copyright of the exam board. How Oracle Prep builds its content