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Suppose that the captain of a ship that is in distress must send a total of eleven different signals in succession. The eleven signals comprise of 4 blue light signals (B1, B2, B3 and B4), 4 purple light signals (P1, P2, P3 and P4) and 3 red light signals (R1, R2 and R3). He must send the signals one after another at 1 minute intervals. In how many different ways may the captain send the signals if the purple light signals are the first 4 signals to be sent and the blue light signals are the last 4 signals?