Explanation

(d)
We know a leap year is fallen within 4 yr, so its probability $= \frac{25}{100} = \frac{1}{4}.$
In a century the probability of $53rd$ Sunday in a leap year $= \frac{1}{4} \times \frac{2}{7} = \frac{2}{28}$
Non-leap year in century = 75
Probability of selecting is non-leap year $= \frac{75}{100} = \frac{3}{4}$
$53rd$ Sunday in non-leap year $= \frac{1}{7}$
Similarly, in a century probabilities of $53rd$ Sunday in a non-leap year
$= \frac{3}{4} \times \frac{1}{7} = \frac{3}{28}$
$\therefore$ Required probability $= \frac{2}{28} + \frac{3}{28} = \frac{5}{28}$