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The roof of a certain bell tower is in the shape of a square pyramid : Multiple-choice Questions — Select One Answer Choice

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Re: The roof of a certain bell tower is in the shape of a square pyramid [#permalink]
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juangg wrote:
Since it is a square pyramid, we need to cover 4 triangle-shaped faces. The problem gives us the length of the base (20) and the height (18) for each of these triangles. Since 1ft = 12 inches, we have the area of each triangle is (1/2)*(18*12)*(20*12) = 25,920 square inches.

Assuming 20% extra surface for overlap, and multiplying by 4 to cover all 4 faces, we have the total surface to be covered is 1.2*4*25,920 = 124,416.

Finally, using the fact that each tile measures 72 square inches, we divide and get 124,416/72 = 1,728.

However, the OA is 1,440, which is identical to everything I did here but for taking the 20% extra surface that the problem says is needed.

I appreciate it if someone can point out where I am making a mistake.


juangg
Think it the other way, Lateral height is the length of two eqaul sides of trianglular face (isosceles triangles), not the height of the triangular face.
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Re: The roof of a certain bell tower is in the shape of a square pyramid [#permalink]
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KarunMendiratta wrote:
juangg wrote:
Since it is a square pyramid, we need to cover 4 triangle-shaped faces. The problem gives us the length of the base (20) and the height (18) for each of these triangles. Since 1ft = 12 inches, we have the area of each triangle is (1/2)*(18*12)*(20*12) = 25,920 square inches.

Assuming 20% extra surface for overlap, and multiplying by 4 to cover all 4 faces, we have the total surface to be covered is 1.2*4*25,920 = 124,416.

Finally, using the fact that each tile measures 72 square inches, we divide and get 124,416/72 = 1,728.

However, the OA is 1,440, which is identical to everything I did here but for taking the 20% extra surface that the problem says is needed.

I appreciate it if someone can point out where I am making a mistake.


Think it the other way, Lateral height is the length of two eqaul sides of trianglular face (isosceles triangles), not the height of the triangular face.


I see. Makes sense now. Thank you for your help!
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Re: The roof of a certain bell tower is in the shape of a square pyramid [#permalink]
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