Note : The two events R and W are ‘disjoint’ events.
Example What is the chance that a leap
year selected at random will contain 53 Sundays ?
Solution : A leap year has 52 weeks and 2 more days.
The two days can be :
Monday  Tuesday
Tuesday  Wednesday
Wednesday  Thursday
Thursday  Friday
Friday  Saturday
Saturday  Sunday and
Sunday
 Monday.
There are 7 outcomes and
2 are favorable to the 53rd
Sunday.
Now for 53 Sundays in a leap year, P(A)
Example If four ladies and six gentlemen
sit for a photograph in a row at random, what is the probability
that no two ladies will sit together ?
Solution : Now
if no two ladies are to be together, the ladies have 7 positions,
2 at ends and 5 between the gentlemen
Arrangement
L, G1, L, G2, L, G3, L, G4, L, G5, L, G6, L
[next page]
