12, 36, 90, 180, 270, 405, 135,
Find the wrong number in the following number series.

The correct answer is 405.

Step-by-step Explanation:

Let us analyze the pattern of multiplication between consecutive terms in the given series:

12, 36, 90, 180, 270, 405, 135

We observe that each successive term is obtained by multiplying the previous term by a factor that decreases by 0.5 at each step:

$12\times 3.0=36$

$36\times 2.5=90$

$90\times 2.0=180$

$180\times 1.5=270$

$270\times 1.0=270$

$270\times 0.5=135$

Following this rule, the term after 270 should be $270\times 1.0=270$, and subsequently $270\times 0.5=135$.

However, the given sequence includes 405 in place of 270.

Therefore, 405 is the wrong number in the series.