To find out how many square inches of icing are needed to cover the cake, we need to calculate the surface area of the top and sides of the cylinder (which represents the cake).
The formula for the surface area \( A \) of a cylinder (not including the bottom, since you want to ice the top and sides) is given by:
\[ A = 2\pi rh + \pi r^2 \]
Where:
- \( r \) is the radius
- \( h \) is the height
- The first term \( 2\pi rh \) calculates the lateral surface area (sides).
- The second term \( \pi r^2 \) calculates the area of the top.
Given:
- Radius \( r = 5 \) in
- Height \( h = 7 \) in
- Use \( \pi \approx 3.14 \)
Now, substitute the values into the formula:
- Calculate the lateral surface area:
\[ \text{Lateral area} = 2\pi rh = 2 \times 3.14 \times 5 \times 7 \]
\[ = 2 \times 3.14 \times 35 \]
\[ = 6.28 \times 35 = 219.8 \text{ square inches} \]
- Calculate the area of the top:
\[ \text{Top area} = \pi r^2 = 3.14 \times 5^2 \]
\[ = 3.14 \times 25 = 78.5 \text{ square inches} \]
- Add the lateral area and the top area to get the total surface area:
\[ A = 219.8 \text{ square inches} + 78.5 \text{ square inches} = 298.3 \text{ square inches} \]
Therefore, the total area of icing needed to cover the sides and top of the cake is 298.3 square inches (to the nearest tenth).