Math Problem Statement

Lindsey made a model of a house in construction class. The block of wood for the base measures 4 in. by 13 in. and is 8 in. tall. She used a triangular prism for the roof that hangs over the base by half an inch on all sides and is 4 in. in height. Lindsey would like to paint the entire model. For the surface area of the model house to determine how much paint would be needed. Assume the roof is the same on both sides. (Hint don't forget about painting underneath the overhang and house bottom) Round your answer up to the nearest whole number.

Solution

To determine the surface area of Lindsey's model house, we'll calculate the surface area of the base (rectangular prism) and the roof (triangular prism), and then add them together.

Step 1: Calculate the Surface Area of the Rectangular Prism (Base)

The dimensions of the base are:

  • Length = 13 inches
  • Width = 4 inches
  • Height = 8 inches

Surface area of the rectangular prism: Surface Arearectangular prism=2lw+2lh+2wh\text{Surface Area}_{\text{rectangular prism}} = 2lw + 2lh + 2wh Substitute the values: =2(13×4)+2(13×8)+2(4×8)= 2(13 \times 4) + 2(13 \times 8) + 2(4 \times 8) =2(52)+2(104)+2(32)= 2(52) + 2(104) + 2(32) =104+208+64=376 square inches= 104 + 208 + 64 = 376 \text{ square inches}

Step 2: Calculate the Surface Area of the Triangular Prism (Roof)

The roof is a triangular prism that hangs over the base by 0.5 inches on all sides.

The new dimensions for the roof are:

  • Length = 13+2×0.5=1413 + 2 \times 0.5 = 14 inches
  • Width (base of the triangle) = 4+2×0.5=54 + 2 \times 0.5 = 5 inches
  • Height of the triangle = 4 inches
  • Height of the prism (length of the roof) = 14 inches

Find the area of one triangular face: Using the formula for the area of a triangle A=12×base×heightA = \frac{1}{2} \times \text{base} \times \text{height}, Atriangle=12×5×4=10 square inchesA_{\text{triangle}} = \frac{1}{2} \times 5 \times 4 = 10 \text{ square inches} Since there are two triangular faces, Area of both triangles=2×10=20 square inches\text{Area of both triangles} = 2 \times 10 = 20 \text{ square inches}

Find the area of the three rectangular faces (sides): Each of these faces is a rectangle with area length×width\text{length} \times \text{width}:

  1. First rectangular face: 14×4=5614 \times 4 = 56 square inches

  2. Second rectangular face: 14×42+2.5214 \times \sqrt{4^2 + 2.5^2} (the slant height)

    Calculate the slant height using Pythagoras' theorem: Slant height=42+2.52=16+6.25=22.254.72 inches\text{Slant height} = \sqrt{4^2 + 2.5^2} = \sqrt{16 + 6.25} = \sqrt{22.25} \approx 4.72 \text{ inches} Then the area is: 14×4.7266.08 square inches14 \times 4.72 \approx 66.08 \text{ square inches}

  3. The third face has the same area as the second, so it also contributes approximately 66.08 square inches.

Thus, the total area of the three rectangular faces is: 56+66.08+66.08=188.16 square inches56 + 66.08 + 66.08 = 188.16 \text{ square inches}

Total surface area of the triangular prism: Surface Areatriangular prism=20+188.16=208.16 square inches\text{Surface Area}_{\text{triangular prism}} = 20 + 188.16 = 208.16 \text{ square inches}

Step 3: Combine the Surface Areas

Finally, the total surface area of the house is: Total Surface Area=376+208.16=584.16 square inches\text{Total Surface Area} = 376 + 208.16 = 584.16 \text{ square inches} Rounding up to the nearest whole number, the total surface area is approximately 585 square inches.

This is the amount of surface area Lindsey will need to paint.

Would you like any further details or clarifications?


Here are 5 related questions:

  1. How would the surface area change if the height of the house base was increased by 2 inches?
  2. What would the volume of the entire house model be?
  3. How would the surface area calculation differ if the roof did not overhang the base?
  4. What is the area of the roof alone without the overhang?
  5. How would changing the overhang distance affect the total surface area?

Tip: When working with models or real objects, always remember to account for all visible surfaces, including the undersides of overhangs or bases when calculating the surface area.

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Math Problem Analysis

Mathematical Concepts

Geometry
Surface Area Calculations
Triangular Prism

Formulas

Surface area of a rectangular prism
Area of a triangle

Theorems

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Suitable Grade Level

Grades 7-9