4MA1/1H Jun 2020, Question 24: Sum of an Arithmetic Series
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1H (Higher) · Calculator · 4 marks
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The question, in short
An arithmetic sequence begins 8, 15, 22, 29, 36. Find the total of the terms from the 50th to the 100th term inclusive.
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Solution · 4 marks
- 1a = 8, d = 7
- 2S_100 = (100/2) * (2*8 + (100 − 1)*7) = 35450
- 3S_49 = (49/2) * (2*8 + (49 − 1)*7) = 8624
- 4Sum from 50th to 100th term = S_100 − S_49
- 535450 − 8624 = 26826
Answer26 826
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