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Geometry and Trigonometry Difficulty: Easy
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In the figure shown, triangle J K L is similar to triangle R S T , where J corresponds to R and K corresponds to S . The length of JK¯ is 15 , and the perimeter of triangle J K L is 36 . The length of RS¯ is 135 . What is the perimeter of triangle R S T ?

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Explanation

Choice A is correct. It’s given that triangle JKL is similar to triangle RST, where J corresponds to R and K corresponds to S. It follows that JK¯ corresponds to RS¯. If two triangles are similar, then the scale factor between their perimeters is equal to the scale factor between the lengths of their corresponding sides. It's given that the length of JK¯ is 15 and the length of RS¯ is 135. Therefore, the scale factor from the length of JK¯ to the length of RS¯ is 13515, or 9. It’s given that the perimeter of triangle JKL is 36. Let p represent the perimeter of triangle RST. It follows that p36=9. Multiplying each side of this equation by 36 yields p=324. Therefore, the perimeter of triangle RST is 324.

Choice B is incorrect and may result from conceptual or calculation errors.

Choice C is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect and may result from conceptual or calculation errors.