Edexcel IGCSEAdditional MathematicsGeneral Applications5 Marks
The nth term of an arithmetic series is uₙ = 5n - 2. (a) Write down the first three terms of the series. (b) Find the sum of the first 20 terms of the series.
- (a)Write down the first three terms of the series.[2]
- (b)Find the sum of the first 20 terms of the series.[3]
Mark scheme
Marking points from the official mark scheme. The mark or mark type is shown in brackets.
- (a)
- B1 for u₁ = 3. (May be implied)
- B1 for u₂ = 8 and u₃ = 13. (Must be all three correct)
- (b)
- M1 for finding the common difference d=5 (may be implied by formula use) or u₂₀ = 5(20) - 2 = 98.
- M1 for using the sum formula Sₙ = n/2(2a + (n-1)d) or Sₙ = n/2(a + l) with their values.
- A1 for S₂₀ = 20/2(3 + 98) = 10(101) = 1010. (cao)
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