RRB Junior Engineer Stage 1 Model Papers 7

Let the total number of students in the class be x. Common Students = 40
$\frac{72\mathit{x}}{100}-40+40+\frac{44\mathit{x}}{100}=\mathit{x}$
$\Rightarrow \frac{72\mathit{x}}{100}\mathit{x}+\frac{44\mathit{x}}{100}\mathit{x}=40$
$\Rightarrow \frac{16\mathit{x}}{100}=40\Rightarrow \mathit{x}=\frac{40\times 100}{16}$
$\Rightarrow \mathit{x}=250$
Alternate Method:
Number persons in both = number of persons in 1st + no. of persons in 2nd – Total no. of persons in any one % of persons in both $=72+44\mathit{–}100=16\%$
Total no. of persons $\times \frac{16}{100}=40$
Total no. = 250