SSC CGL 24 Aug 2021 Shift 2 Paper

First ten positive odd numbers
$=1,3,5........$
$\mathit{S}{\mathit{n}}_1=\frac{\mathit{n}}{2}\left[2\mathit{a}+\left(\mathit{n}-1\right)\mathit{d}\right]$
Here, $\mathit{a}=1,\mathit{d}=3-1=2$
$\mathit{n}=10=$ Number of terms
$=\frac{10}{2}\left[2\times 1+\left(10-1\right)2\right]$
$\mathit{S}{\mathit{n}}_1=5\times 20=100$
$\therefore$ Average of first ten positive odd
numbers $=\frac{100}{10}=10$
First 15 even number,
$\mathit{S}\mathit{n}=$ Sum of numbers.
$\mathit{S}{\mathit{n}}_2=\frac{\mathit{n}}{2}\left[2\mathit{a}+\left(\mathit{n}-1\right)\mathit{d}\right]$
$\mathit{a}=2,\mathit{d}=4-2=2,\mathit{n}=15$
$\therefore 2,4,6..........$
${\mathit{S}\mathit{n}}_2=\frac{15}{2}\left[2\times 2+\left(15-1\right)2\right]$
$=\frac{15}{2}\left[4+28\right]$
$=\frac{15}{2}\times 32$
$=15\times 16$
Average $=\frac{15\times 16}{15}=16$
Product of $\mathit{S}{\mathit{n}}_1\times \mathit{S}{\mathit{n}}_2=10\times 16=160$.