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If the sum of the second, fourth and sixth terms of a G.P. of positive terms is 21 and the sum of eighth, tenth and twelfth terms is 15309, then the sum of its first nine terms is: (1) 755 (2) 750 (3) 760 (4) 757

1. 755
2. 750
3. 760
4. 757

Correct answer: 757

Solution

The correct option is right because the relationships between the terms of the geometric progression allow us to derive the first term and the common ratio, leading to the accurate calculation of the sum of the first nine terms, which is 757.

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