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How many sequences of colors are possible...You pass through five traffic signals on your way to work. Each is either red, yellow, or green. A red is always immediately followed by a yellow; a green is never followed immediately by a green. How many sequences of colors are possible for the five signals? |

Re: How many sequences of colors are possible...Just draw a game tree and count the number of different outcomes. Can the last light be red? It seems not. Alternatively, keep a count of (R)ed, (Y)ellow, (G)reen, and in each row let new R = Y+G, new Y = R+Y+G, and new G = Y. 1, 1, 1 2, 3, 1 4, 6, 3 etc |

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