P(B|A) = P(A B)/P(A)
P(B|A) = (12/15)/(2/15) = 6.
If P(A) = 2/15, P(B) = 4/15, and P(A B) = 12/15 Find P(B|A)
Options:
(A) 1/2
(B) 2/3
(C) 3/2
(D) 4/5
(E) 6
(E)

Speed of the train in metres/sec = 72000/3600 = 20
Distance travelled by train to cross the platform = 30 * 20 = 600 = Length of train + Length of platform
Distance travelled by train to cross the man = 19 * 20 = 380 = Length of train
Length of platform = 600 - 380 = 220
A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 19 seconds. What is the length of the platform in meters?
Options:
(A) 220 meters
(B) 360 meters
(C) 420 meters
(D) 600 meters
(E) Cannot be determined
(A)

Bunuel, I'm also a little confused with the number of arrangements of n distinct objects in a circle. Why is it given by (n-1)!. In theveritasanswer they say:answer E (6050), should be the number of ways to arrange all 7 without the seating restriction given. Is this incorrect?
At a meeting of the 9 Joint Chiefs of Staff, the Chief of Naval Operations does not want to sit next to the Chief of the National Guard Bureau. How many ways can the 9 Chiefs of Staff be seated around a circular table?
Options:
(A) 120
(B) 480
(C) 960
(D) 2520
(E) 6050
(E)