Three fair six-sided dice are rolled. What is the probability that the

Total number of cases possible when 3 Dice roll= 6^3=216
Now we have to find the number of cases when values shown on two of the dice sum to the value shown on the remaining die-
1. When a dice shows 6, other 2 dices must show either (5,1) or (4,2) or (3,3)
Total number of cases possible in this scenario= 3!+3!+3!/2!=15
2. When a dice shows 5, other 2 dices must show either (4,1) or (3,2)
Total number of cases possible in this scenario= 3!+3!=12
3. When a dice shows 4, other 2 dices must show either (3,1) or (2,2)
Total number of cases possible in this scenario= 3!+3!/2!=9
4. When a dice shows 3, other 2 dices must show (2,1)
Total number of cases possible in this scenario= 3!=6
5. When a dice shows 2, other 2 dices must show (1,1)
Total number of cases possible in this scenario= 3!/2!=3
Total cases possible= 15+12+9+6+3=45

Prbability= 45/216=5/24