Select the number that can replace the question mark in the given number series 121 57 21 5 ........

Logical Reasoning (MTS) Number series

Select the number that can replace the question mark (?) in the given number series.

121, 57, 21, 5, ?

This questions was previously asked in

SSC MTS 11th October 2021 Shift-3

- Start with the series: 121, 57, 21, 5, ?

- Observe the pattern: each number is derived by a function applied to the previous one.

- Examine differences:

- \(121 - 57 = 64\) equals \(8^2\).

- \(57 - 21 = 36\) equals \(6^2\).

- \(21 - 5 = 16\) equals \(4^2\).

- Recognize a pattern reducing squares by 2: \(8, 6, 4, \ldots\).

- Predict that the next difference is \(2^2 = 4\).

- Calculate: \(5 - 4 = 1\).

- The number replacing the question mark is 1.

Option 3: 1 is correct.

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