AI Tutor
Imagine wrapping a gift box that measures 4.5 cm4.5\text{ cm} wide, 3 cm3\text{ cm} long, and 2.5 cm2.5\text{ cm} tall. How much wrapping paper do you actually need to cover every single side without overlapping?
To find out, we need to calculate the surface area, which is the total area of all the flat outside faces of a 3D shape.
What does a 3D box look like if you slice along the edges and unfold it flat?

Unfolding Prisms into Nets

A net is a two-dimensional flat pattern that folds up to make a three-dimensional figure.
When the side lengths are decimals or fractions, we call them rational dimensions — any numbers that can be written as a ratio of integers.
Notice that opposite faces are identical pairs: two matching tops/bottoms, two matching fronts/backs, and two matching left/right sides.
How do we turn these unfolded rectangles into exact decimal calculations?

Rectangular Prisms with Decimals

The total surface area (SS) is the sum of all six faces. We calculate the area of each pair of matching faces using Area=length×width\text{Area} = \text{length} \times \text{width}:
Top and Bottom=2×(4.5×3)=2×13.5=27 cm2\text{Top and Bottom} = 2 \times (4.5 \times 3) = 2 \times 13.5 = 27\text{ cm}^2
Front and Back=2×(4.5×2.5)=2×11.25=22.5 cm2\text{Front and Back} = 2 \times (4.5 \times 2.5) = 2 \times 11.25 = 22.5\text{ cm}^2