NIMCET 2016 Question Paper with solutions

We can check it through option.
If x is the number of children in 1 st row.
then in 2nd row = (x - 3) children
in 3rd row = (x - 6) children
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6th row = (x -15) children
$\therefore \mathit{x}+\mathit{x}-3+\mathit{x}-6+\mathit{x}-9+\mathit{x}-12+\mathit{x}-15=630$
$\Rightarrow 6\mathit{x}-45=630$
$\Rightarrow 6\mathit{x}=675$
$\Rightarrow \mathit{n}=\frac{675}{6}=112.5$
So, 6 row is not possible as number of children cannot be in fraction.