To determine the surface area of the box that needs to be decorated, we start with the dimensions provided: length (L) = 27 cm, width (W) = 20 cm, and height (H) = 20 cm.
The box has the following surfaces:
- Front: 27 cm (length) × 20 cm (height)
- Left side: 20 cm (width) × 20 cm (height)
- Right side: 20 cm (width) × 20 cm (height)
- Top: 27 cm (length) × 20 cm (width)
Since the bottom and back do not need to be decorated, we will calculate the surface areas of the front, left side, right side, and top.
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Area of the front: \[ \text{Area}_{\text{front}} = L \times H = 27 , \text{cm} \times 20 , \text{cm} = 540 , \text{cm}^2 \]
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Area of the left side: \[ \text{Area}_{\text{left}} = W \times H = 20 , \text{cm} \times 20 , \text{cm} = 400 , \text{cm}^2 \]
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Area of the right side: \[ \text{Area}_{\text{right}} = W \times H = 20 , \text{cm} \times 20 , \text{cm} = 400 , \text{cm}^2 \]
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Area of the top: \[ \text{Area}_{\text{top}} = L \times W = 27 , \text{cm} \times 20 , \text{cm} = 540 , \text{cm}^2 \]
Now, sum these areas to find the total surface area that needs decorating:
\[ \text{Total Surface Area} = \text{Area}{\text{front}} + \text{Area}{\text{left}} + \text{Area}{\text{right}} + \text{Area}{\text{top}} \]
\[ \text{Total Surface Area} = 540 , \text{cm}^2 + 400 , \text{cm}^2 + 400 , \text{cm}^2 + 540 , \text{cm}^2 \]
Now compute the final sum:
\[ \text{Total Surface Area} = 540 + 400 + 400 + 540 = 1880 , \text{cm}^2 \]
Thus, the surface area of the box that needs to be decorated is 1880 cm².