A-LevelMathematicsSeries9709/12 · May/June 2022 · Q45 Marks
The first, second and third terms of an arithmetic progression are k, 6k and k + 6 respectively.
- (a)Find the value of the constant k.[2]
- (b)Find the sum of the first 30 terms of the progression.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.
- [B1] 2 × 6k = k + k + 6 or 6k – k = k + 6 – 6k or 2d = 6 leading to d = 3, .: 6k – 3 = k
- [B1] k = 6/10 or 0.6
- [B1] d = 3
- [M1] S₃₀ = (30/2)(2 × 'their k' + 29 × 'their d')
- [A1] S₃₀ = 1323
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