Number Series, Coding, Odd Man OutPYQ July 21Question 2021 of 217
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The wrong term in the series 225,196,169,144,121,100,77,64\displaystyle 225, 196, 169, 144, 121, 100, 77, 64, is:

Options

A121
B77
C100
D169
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Correct Answer

✅ Option b — 77

All Options:

  • A121
  • B77
  • C100
  • D169

Detailed Solution & Explanation

We are given the series: 225,196,169,144,121,100,77,64\displaystyle 225, 196, 169, 144, 121, 100, 77, 64
Let's express each term as a perfect square:
- 225=152\displaystyle 225 = 15^2
- 196=142\displaystyle 196 = 14^2
- 169=132\displaystyle 169 = 13^2
- 144=122\displaystyle 144 = 12^2
- 121=112\displaystyle 121 = 11^2
- 100=102\displaystyle 100 = 10^2
- 77\displaystyle 77 (not a perfect square)
- 64=82\displaystyle 64 = 8^2
The sequence consists of squares of descending consecutive natural numbers: 152,142,132,122,112,102,92,82\displaystyle 15^2, 14^2, 13^2, 12^2, 11^2, 10^2, 9^2, 8^2.
The seventh term should be 92=81\displaystyle 9^2 = 81 instead of 77\displaystyle 77.
Therefore, 77\displaystyle 77 is the wrong/incorrect term in the series.
Hence, **Option B** is the correct answer.

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