Multiple choice

In the following number series one numbers is wrong. Find the wrong number ? 12, 24, 39, 57, 79, 102, 129

  1. 12

  2. 39

  3. 79

  4. 102

  5. 129
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C Correct answer
Explanation

Pattern: differences are +12, +15, +18, +22, +23, +27. Expected: +12, +15, +18, +21, +24, +27. With +21 at position 4: 57+21=78, then 78+24=102, 102+27=129. The actual term is 79 instead of 78, so 79 is wrong. Or using n²+(n+10): 12=1²+11, 24=3²+15, 39=5²+14(no), 57=7²+8... 79=8²+15, but pattern breaks.

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