Number Series, Coding, Odd Man OutPYQ Dec 22Question 2029 of 217
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Find the missing number in the following series? 3,5,5,19,7,41,9,?,11,109\displaystyle 3, 5, 5, 19, 7, 41, 9, ?, 11, 109

Options

A71
B61
C69
D79
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Correct Answer

✅ Option a — 71

All Options:

  • A71
  • B61
  • C69
  • D79

Detailed Solution & Explanation

We are given the series: 3,5,5,19,7,41,9,?,11,109\displaystyle 3, 5, 5, 19, 7, 41, 9, ?, 11, 109
Let's split this series into two alternating sequences:
1. **Odd-positioned terms (1st, 3rd, 5th, 7th, 9th):**
- 3,5,7,9,11\displaystyle 3, 5, 7, 9, 11
- Pattern: consecutive odd numbers starting from 3\displaystyle 3 (common difference +2\displaystyle +2).
2. **Even-positioned terms (2nd, 4th, 6th, 8th, 10th):**
- 5,19,41,?,109\displaystyle 5, 19, 41, ?, 109
- Let's compute the differences between these consecutive terms:
- 19−5=14\displaystyle 19 - 5 = 14
- 41−19=22\displaystyle 41 - 19 = 22
- Notice that the differences increase by 8\displaystyle 8 each time (14+8=22\displaystyle 14 + 8 = 22).
- The next difference should be 22+8=30\displaystyle 22 + 8 = 30.
- The missing term (at the 8th position) is:
41+30=7141 + 30 = 71
- Let's check the next term in the sequence using a difference of 30+8=38\displaystyle 30 + 8 = 38:
71+38=10971 + 38 = 109
This matches the 10th term perfectly!
Hence, **Option A** is the correct answer.

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