Two players, P1 and P2, play a game against each other. In every round of the game, each player rolls a fair die once, where the six faces of the die have six distinct numbers. Let x and y denote the readings on the die rolled by P1 and P2, respectively. If x > y, then P1 scores 5 points and P2 scores 0 point. If x = y, then each player scores 2 points. If x < y, then P1 scores 0 point and P2 scores 5 points. Let Xi and Yi be the total scores of P1 and P2, respectively, after playing the ith round.
| List-I | List-II |
|---|---|
| (I) Probability of X2 ≥ Y2 is | (P) |
| (II) Probability of X2 > Y2 is | (Q) |
| (III) Probability of X3 = Y3 is | (R) |
| (IV) Probability of X3 > Y3 is | (S) |
| (T) |
The correct option is :
Correct Answer :
(I) → (Q); (II) → (R); (III) → (T); (IV) → (S)
Solution :
The correct option is (I) → (Q); (II) → (R); (III) → (T); (IV) → (S).
Understanding the Game Dynamics:
In each round, two players P1 and P2 roll a standard fair 6-sided die once. Let the outcome of P1's roll be x and P2's roll be y.
Since the die has 6 distinct faces and is fair, each of the 36 possible ordered pairs (x, y) is equally likely with a probability of .
The rules for scoring in any single round are:
1. Case 1: x = y (Tie)
There are 6 such outcomes: (1,1), (2,2), (3,3), (4,4), (5,5), (6,6).
Probability of tie: P(x = y) = .
Points awarded: P1 gets 2 points, P2 gets 2 points.
2. Case 2: x > y (P1 wins the round)
Number of outcomes where x > y is .
Probability of P1 winning: P(x > y) = .
Points awarded: P1 gets 5 points, P2 gets 0 points.
3. Case 3: x < y (P2 wins the round)
Number of outcomes where x < y is 15.
Probability of P2 winning: P(x < y) = .
Points awarded: P1 gets 0 points, P2 gets 5 points.
Part (I): Probability of X2 ≥ Y2
Let Xi and Yi be the total scores of P1 and P2 after round i.
By symmetry between players P1 and P2:
Also, the total probability space covers:
Thus, .
Using symmetry, .
X2 = Y2 occurs only if:
- Both rounds are ties: Probability =
- One round is won by P1 and one round is won by P2 (in any order): Probability =
Therefore,
Now, calculate P(X2 ≥ Y2):
Hence, (I) → (Q).
Part (II): Probability of X2 > Y2
Using the values derived above:
Hence, (II) → (R).
Part (III): Probability of X3 = Y3
After 3 rounds, P1 and P2 will have equal total scores (X3 = Y3) if and only if:
- All 3 rounds end in ties: Probability =
- Exactly 1 round is a tie, 1 round won by P1, and 1 round won by P2. The number of permutations for these 3 outcomes is 3! = 6:
Probability =
Summing these probabilities:
Hence, (III) → (T).
Part (IV): Probability of X3 > Y3
By symmetry between P1 and P2:
Substituting :
Hence, (IV) → (S).
Combining all the matches:
(I) → (Q)
(II) → (R)
(III) → (T)
(IV) → (S)
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