The probability that in a year of the 22nd century choosen at random, there will be 53 Sundays is: |
$\frac{3}{28}$ $\frac{2}{7}$ $\frac{5}{28}$ $\frac{1}{7}$ |
$\frac{5}{28}$ |
The correct answer is Option (3) → $\frac{5}{28}$ Consider a year of 365 days (non-leap) or 366 days (leap year). Number of weeks = 52 weeks + 1 day (non-leap) or +2 days (leap) Non-leap year (365 days): 52 full weeks → 52 Sundays guaranteed, 1 extra day → if the extra day is Sunday → 53 Sundays Probability = 1/7 Leap year (366 days): 52 full weeks → 52 Sundays guaranteed, 2 extra days → if one of the two days is Sunday → 53 Sundays Probability = 2/7 Number of leap years in 22nd century (2101–2200) = 25 (every 4th year except years divisible by 100 not divisible by 400) Number of non-leap years = 100 - 25 = 75 Total probability: $P = \frac{75*(1/7) + 25*(2/7)}{100} = \frac{75+50}{700} = \frac{125}{700} = \frac{5}{28}$ Answer: $\frac{5}{28}$ |