Student: There are five same model cars parked in the same direction in parking. If 3 cars are red, 1 is black and 1 is green, in how many ways they can be arranged in the parking?\nOptions:\n(A) 10 ways.\n(B) 20 ways.\n(C) 30 ways.\n(D) 40 ways.\n(E) 50 ways..
Another student: Let's say, hmmm...

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5!/(3!*1!*1!) = (5*4*3*2*1)/(3*2*1) = 120/6 = 20 ways. Final answer: (B).
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