Geometric progression (term index): Find which term equals 1280. Series definition: 5, 10, 20, 40, … (each term doubles the previous). Determine the term number n for which the value is 1280. Choose the correct index.
Verbal Reasoning
Series Completion
Difficulty: Easy
Choose an option
-
A10th
-
B9th
-
C8th
-
DNone of these
Answer
Correct Answer: 9th
Explanation
Modeltn = 5 × 2n−1.
Solve for n5 × 2n−1 = 12802n−1 = 1280 / 5 = 256 = 28n − 1 = 8 ⇒ n = 9
Final Answer9th