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Let a 1 , a 2 , a 3 , ……. be a G.P. such that a 1 < 0, a 1 + a 2 = 4 and a 3 + a 4 = 16. If ∑ = 9 1 i i a = 4 λ , then λ is equal to:

1. 3 511
2. –171
3. –513
4. 171

Correct answer: –171

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