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## #1 2017-02-08 09:58:28

### Which term of the series 5, 10, 20, 40, ... is 1280?

# Aptitude Quizzes Mathematics Aptitude Test

**Question:**

Which term of the series 5, 10, 20, 40, ... is 1280?

**Option A):**

None of these**Option B):**

10th**Option C):**

9th**Option D):**

8th

**Correct Answer is Option C):**

9th

**Explanation:**

Clearly, 5x2 = 10,10x2 = 20, 20x2 =40 So. the series is a G.P. in which a = 5 and r = 2. Let the number of terms be n. Then, 5x2(power n-1) = 1280 => 2(power n-1) = 256 = 2(power n). :. n—1 = 8 or n = 9

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## 2017-02-08 09:58:28

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