Find the sum of the first 20 terms of the sequence 2, 3, 5, 7, 8, 11, …
Explanation:
The given sequence is a combination of two APs.
The first AP is (2, 5, 8, …) and the second AP is (3, 7, 11, … )
∴ Sum = 10/2 × (2 × 2 + 9 × 3) + 10/2 × (2 × 3 + 9 × 4) = 365
Hence, 365.
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