Symbiosis National Aptitude Test SNAP 2014 Paper

Total number of balls = 8. Let the first drawn ball is white, so required probability = $\frac{5}{8}\times \frac{3}{7}\times \frac{4}{6}\times \frac{2}{5}$ = $\frac{1}{14}$.
But here we had started with a white ball. When we start with a black ball, the required probability
= $\frac{3}{8}\times \frac{5}{7}\times \frac{2}{6}\times \frac{4}{5}$ = $\frac{1}{14}$.
Since these two cases are mutually exclusive.
Total probability = $\frac{1}{14}+\frac{1}{14}$ = $\frac{2}{14}$ = $\frac{1}{7}$