Answer:
A) 0.5
B) 0.375
C) 0.375
D) 0.167
Explanation:
Let's call
a: Ariel
b: Bob
c: Chris
d: Diana
There are 4*3*2*1 = 24 total combinations to order the 4 children
A) Ariel is older than Diana in the following 12 cases:
a b c d
a b d c
a c b d
a c d b
a d b c
a d c b
b a c d
b a d c
b c a d
c a b d
c a d b
c b a d
Then, the probability is 12/24 = 0.5
B) The condition "Ariel is older than Diana, if it is given that Ariel is older than Bob" is satisfied in the six first cases and last three cases of before.
Then, the probability is 9/24 = 0.375
C) Ariel is older than Diana, if it is given that Chris is older than Diana, in the following cases:
a b c d
a c b d
a c d b
a d c b
b a c d
b c a d
c a b d
c a d b
c b a d
Then, the probability is 9/24 = 0.375
D) Ariel is older than Diana, if it is given that Diana is older than Bob, in the following cases:
a c d b
a d b c
a d c b
c a d b
Then, the probability is 4/24 = 0.167