Find subgame Nash equilibrium

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Two players, A and B play the following game. First A must choose IN or OUT. If A chooses OUT, then the game ends, and the payoffs are: A gets 2 and B gets 0. If A chooses IN, then B observes this and must then choose IN or OUT. If B chooses OUT, then the game ends, and the payoffs are: A gets 0 and B gets 2. If A chooses IN and B chooses IN, then they play the following simultaneous move game:

                    Player 2
                    L      R 
    Player 1:  U  3, 1   0, -2
               D  -1, 2  1, 3 

Find all the pure-strategy subgame perfect Nash equilibria of the game.

I'm not sure if my answer is correct: A will choose OUT, B will choose IN when A and B selects D and R respectively, B will choose OUT when A and B select U and L respectively.

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Your answer is correct, as can be confirmed by backward induction starting at the simultaneous move. The formulations "will choose" and "when A and B select" are somewhat misleading, since these choices will not actually occur, as the game ends after A chooses OUT. These are merely the players' strategies for these choices.