Problem:
Small lights are hung on a string 6 inches apart in the order red, red, green, green, green, red, red, green, green, green, and so on continuing this pattern of 2 red lights followed by 3 green lights. How many feet separate the 3 rd red light and the 21st red light?
Note: 1 foot is equal to 12 inches.
Answer Choices:
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Solution:
Consider consecutive red, red, green, green, green lights as a unit. There are feet between corresponding lights in successive units. The 3rd red light begins the 2nd unit, and the 21st red light begins the 11th unit. Therefore the distance between the desired lights is feet.
The problems on this page are the property of the MAA's American Mathematics Competitions