Question Details

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-IList-II
(I) Probability of X2 ≥ Y2 is(P) 38
(II) Probability of X2 > Y2 is(Q) 1116
(III) Probability of X3 = Y3 is(R) 516
(IV) Probability of X3 > Y3 is(S) 355864
(T) 77432

The correct option is :

Options

A

(I) → (Q); (II) → (R); (III) → (T); (IV) → (S)

B

(I) → (Q); (II) → (R); (III) → (T); (IV) → (T)

C

(I) → (P); (II) → (R); (III) → (Q); (IV) → (S)

D

(I) → (P); (II) → (R); (III) → (Q); (IV) → (T)

Show Answer

Correct Answer :

Option A

(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 136.

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) = 636=16.
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 36-62=15.
Probability of P1 winning: P(x > y) = 1536=512.
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) = 1536=512.
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:

P(X2>Y2)=P(X2<Y2)

Also, the total probability space covers:

P(X2>Y2)+P(X2=Y2)+P(X2<Y2)=1

Thus, P(X2Y2)=P(X2>Y2)+P(X2=Y2).
Using symmetry, P(X2Y2)=1+P(X2=Y2)2.

X2 = Y2 occurs only if:
- Both rounds are ties: Probability = (16)×(16)=136
- One round is won by P1 and one round is won by P2 (in any order): Probability = 2×(512)×(512)=2572

Therefore,

P(X2=Y2)=136+2572=2+2572=2772=38

Now, calculate P(X2 ≥ Y2):

P(X2Y2)=1+382=1116

Hence, (I) → (Q).

Part (II): Probability of X2 > Y2
Using the values derived above:

P(X2>Y2)=1-P(X2=Y2)2=1-382=516

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 = (16)3=1216
- 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 = 6×(16)×(512)×(512)=25144

Summing these probabilities:

P(X3=Y3)=1216+25144=2+75432=77432

Hence, (III) → (T).

Part (IV): Probability of X3 > Y3
By symmetry between P1 and P2:

P(X3>Y3)=1-P(X3=Y3)2

Substituting P(X3=Y3)=77432:

P(X3>Y3)=1-774322=355864

Hence, (IV) → (S).

Combining all the matches:
(I) → (Q)
(II) → (R)
(III) → (T)
(IV) → (S)

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