CAT 2019 Question Paper | Quants Slot 1

CAT Questions

Here is a straightforward question from Series. These are nice questions as they focus on first principles more than mugging up any formulas. If you have a basic feel for numbers, this should be a very doable question. With good CAT Online preparation, you will be able to spot these easy questions even under exam pressure. Hence try this and all the other questions available under the CAT Previous Years Question Paper.

Question 16 : If a₁ + a₂ + a₃ + ... + a_n = 3(2ⁿ⁺¹ - 2), then a₁₁ equals [TITA]

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Video Explanation

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Explanatory Answer

Let n = 1,
a₁ = 3(2¹⁺¹ -2) = 3(4-2) = 6 = 3 x 2¹
a₂ = 3(2²⁺¹ -2) = 3(8-2) = 18, a₂ = 18 - 6 = 12 = 3 x 2²
a₃ = 3(2³⁺¹ -2) = 3(14) = 42 a₃ = 42 - 12 - 6 = 42-18 =24 = 3 x 2³
So, a₁₁ = 3 x 2¹¹ = 3 x 2048
a₁₁ = 6144

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The question is "If a₁ + a₂ + a₃ + ... + a_n = 3(2ⁿ⁺¹ - 2), then a₁₁ equals [TITA] "

Hence, the answer is 6144