What is the chance that a leap year, selected at random, will contain 53 Saturdays? A. 2/7 B. 3/7 C. 1/7 D. 5/7

GATE 2013 · General Aptitude · Probability · medium

Answer: P(53 Saturdays in a leap year) = 2/7. Answer: A. 2/7

1. Determine the structure of a leap year: 366 = 52 * 7 + 2. So there are 52 guaranteed Saturdays plus the 2 leftover days.
2. List the 7 possible extra-day pairs: (Sun,Mon), (Mon,Tue), (Tue,Wed), (Wed,Thu), (Thu,Fri), (Fri,Sat), (Sat,Sun)
3. Count favorable pairs and compute probability: Pairs containing Saturday: (Fri,Sat) and (Sat,Sun). That is 2 out of 7. P = 2/7.