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SSC Selection Post 2022 PYQ — Question 64

SSC Selection Post - Graduation Level 2022 - 4 Aug 2022 - Shift 4 • Quantitative Aptitude • Q64

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The sum of the first 13 terms of a GP is equal to the sum of the first 11 terms in the same GP. The sum of the first 15 terms is 1200. What is the 21st term in the same GP?

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Correct answer: A

Explanation

The correct answer is Option 1 i.e. 1200.

S13 = S11

⇒ a(1 - r13)/(1 - r) = a(1 - r11)/(1 - r)

⇒ r13 = r11

⇒ r2 = 1

⇒ r = - 1

So, S15 = 1200

⇒ a[1 - (- 1)15]/[1 - (- 1)] = 1200

⇒ a(1 + 1)/2 = 1200

⇒ a = 1200

T21 = ar20 = 1200 × (- 1)20 = 1200