praetorian123 wrote:

Rules

1. Time yourself

2. Solve seperately

3. Write your solution here and please mention your time

Two girls have their birthdays in the same Week. It is known that one

of the girls was born on a Saturday. Determine the probability that both

were born on a Saturday.

1/2

1/4

1/7

1/13

1/14

Well, i think this got to everyone. The answer is 1/13.

We know that at least one person has a birthday on Saturday. So for the probability that both were born on a Saturday, i first list the possibilities of birthdays for both girls .

G1-Girl 1

G2-Girl 2

G1 - G2

Sun-Sat

Mon-Sat

Tue-Sat

Wed-Sat

Thu-Sat

Fri-Sat

Sat-Sat
Sat-Sun

Sat-Mon

Sat-Tue

Sat-Wed

Sat-Thu

Sat-Fri

Note, we do not know which girl's birthday is on Saturday. So, we have to fix Each girls birthday on Saturday at a time and then list out the rest of the possibilities.

We have 13 possible combinations. Of those thirteen possible combinations that fulfill the condition, only

one has two Saturdays, hence 1/13.