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A rectangular solid P has height 2c and a base of width a an [#permalink]
17 Dec 2017, 14:15

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A rectangular solid P has height 2c and a base of width a and length b. Two other rectangular solids, Q and R, each have height c and bases of width a and length b. Which of the following represents the amount by which the sum of the surface areas of Q and R exceeds the surface areas of P?

Re: A rectangular solid P has height 2c and a base of width a an [#permalink]
17 Dec 2017, 20:47

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So the formula for the aurface area is 2ab + 2bc + 2ac

Lets replace by values. A= 2 B= 3 and C = 4 The first one is 2(2)(3) + 2(3)(8) + 2(2)(8) = 92 (8 because 2C) The two small ones will have 4 for C. 2(2)(3) + 2(3)(4) + 2(2)(4) = 52 We want to know the surface area for figures so 52 *2 = 104 The difference os 104 -92 = 12 So A