4MA1/2HR Jan 2020, Question 22: Sum of an Arithmetic Series
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2HR (Higher) · Calculator · 4 marks
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The question, in short
An arithmetic series has first term −6 and the sum of its first 30 terms is 2865. Find the 9th term of the series.
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Solution · 4 marks
- 1Sum formula: 2865 = 30/2 × (2 × (−6) + 29d)
- 22865 = 15(−12 + 29d), so 191 = −12 + 29d
- 329d = 203, so d = 7
- 49th term = −6 + 8 × 7 = 50
Answer50
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