CA Foundation · Quantitative Aptitude · Number Series, Coding-Decoding and Odd Man Out
Find the missing term in the series: 3, 8, 18, 38, ?, 158.
The missing term is 78. The rule is to double the previous term and add 2: 3, 8, 18, 38, 78. Working forward from 78 gives 78×2+2=158, which matches the last given term, confirming the answer.
- A68
- B78Correct
- C88
- D98
Explanation
Each term is twice the previous term plus 2: 3×2+2=8, 8×2+2=18, 18×2+2=38, so next is 38×2+2=78. Check: 78×2+2=158, which matches. 68 comes from adding 30 wrongly, and it fails to give 158.
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