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← JEE Advanced 2016 · Paper 2
MathematicsSingle correct+3Question 51 of 54

JEE Advanced 2016 · Paper 2, Mathematics question 51

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PARAGRAPH 1

Football teams T1T_1 and T2T_2 have to play two games against each other. It is assumed that the outcomes of the two games are independent. The probabilities of T1T_1 winning, drawing and losing a game against T2T_2 are 12\frac12, 16\frac16 and 13\frac13, respectively. Each team gets 3 points for a win, 1 point for a draw and 0 point for a loss in a game. Let XX and YY denote the total points scored by teams T1T_1 and T2T_2, respectively, after two games.

P(X>Y)P(X>Y) is

Choose one option
Answer and worked solution

Official answer: B

Per game, T1T_1 wins with probability 12\frac12, draws 16\frac16 and loses 13\frac13.

X>YX>Y happens for:

  • two wins: 14\frac14;
  • a win and a draw, in either order: 2⋅12⋅16=162\cdot\frac12\cdot\frac16=\frac16.

(A win and a loss gives 3-3.)

P(X>Y)=14+16=512.P(X>Y)=\frac14+\frac16=\frac5{12}.

(B)