SSC CHSL 15 Nov 2015 Shift 1 Paper

Let the numbers (in decreasing order) be $\mathit{a},\mathit{b},\mathit{c},\mathit{d},\mathit{e},\mathit{f}$
Average of first 5 = 30
⇒ Sum of first 5 numbers = $30\times 5$
⇒ $\left(\mathit{a}+\mathit{b}+\mathit{c}+\mathit{d}+\mathit{e}\right)=150$ ------(i)
Similarly, sum of last 5 = 25 × 5
⇒$\left(\mathit{b}+\mathit{c}+\mathit{d}+\mathit{e}+\mathit{f}\right)=125$ ----(ii)
Subtracting equation (ii) from equation (i),
⇒ $\mathit{a}-\mathit{f}=150-125=25$
Thus, the differences of the first and the last numbers = 25