Question

Aubrey is making cone-shaped hats for a birthday party. She mistakenly thinks that she will need about 104 square inches of paper for each hat.
Cone with diameter six inches and slant height eight inches.

What is the correct amount of paper Aubrey will need per hat? Explain Aubrey’s mistake. Use 3.14 for π and round to the nearest inch.
A.

About 70 in2; Aubrey found the surface area of the cone, but did not include the base.
B.

About 70 in2; Aubrey used the diameter instead of the radius to find the surface area of a cone.
C.

About 75 in2; Aubrey found the surface area of the cone and included the base.
D.

About 75 in2; Aubrey found the volume of the cone instead of the surface area.

Answer 1

Answer:

C. About 75 in²; Aubrey found the surface area of the cone and included the base.

Step-by-step explanation:

In the questions above we were given the following:

Cone with

Diameter(D) = 6 inches

Slant height (l) = 8 inches.

Aubrey made an error in her calculation.

She found the Total Surface area of the cone using the formula:

Total Surface Area of a cone = πrl + πr²

= πr(l + r)

The Total surface area of a cone is the calculated as Sum of the curved surface area of a cone and the base of the cone.

Where:

Curved surface area of the cone is calculated as = πrl

Base of a cone is calculated as = πr²

Where r = radius of the cone

l = slant height of the cone

In the question, we were given

slant height(l) = 8 inches.

radius = Diameter ÷ 2 = 6÷2 = 3 inches.

Using π = 3.14

Surface area = 3.14 × 3(8+3)

= 9.42 × 11

Surface area = 103.62 in²

Approximately to the nearest inch = 104 in² or 104 square inches.

But this answer is WRONG.

The RIGHT FORMULA Aubrey should have used is

Curved Surface Area or the Lateral Area of a Cone = πrL

slant height(l) = 8 inches.

radius = Diameter ÷ 2 = 6÷2 = 3 inches.

Using π = 3.14

Curved Surface Area of a Cone = πrL

= 3.14 × 3 inches × 8 inches

= 75.36 square inches or 75.36in²

Approximately to the nearest inch = 75 square inches or 75 in².

This is the correct answer.

The error Aubrey made was she calculated the Total surface area of the cone which includes the base of the cone instead of calculating the curved surface area of the cone only.

Hence, from the above calculation , we can see that Option C "About 75 in²; Aubrey found the surface area of the cone and included the base" is the correct option.