### All ACT Math Resources

## Example Questions

### Example Question #11 : Surface Area

What is the surface area of a cone with a radius of 6 in and a height of 8 in?

**Possible Answers:**

96*π* in^{2}

60*π* in^{2}

112*π* in^{2}

36*π* in^{2}

66*π* in^{2}

**Correct answer:**

96*π* in^{2}

Find the slant height of the cone using the Pythagorean theorem: *r*^{2} + *h*^{2} = *s*^{2} resulting in 6^{2} + 8^{2} = *s*^{2} leading to *s*^{2} = 100 or *s* = 10 in

SA = *πrs* + *πr*^{2} = *π*(6)(10) + *π*(6)^{2} = 60*π* + 36*π* = 96*π* in^{2}

60*π* in^{2} is the area of the cone without the base.

36*π* in^{2} is the area of the base only.

### Example Question #1 : How To Find The Surface Area Of A Cone

Use the following formula to answer the question.

The slant height of a right circular cone is . The radius is , and the height is . Determine the surface area of the cone.

**Possible Answers:**

**Correct answer:**

Notice that the height of the cone is not needed to answer this question and is simply extraneous information. We are told that the radius is , and the slant height is .

First plug these numbers into the equation provided.

Then simplify by combining like terms.

### Example Question #2 : How To Find The Surface Area Of A Cone

The slant height of a cone is ; the diameter of its base is one-fifth its slant height. Give the surface area of the cone in terms of .

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone with base of radius and slant height is

.

The diameter of the base is ; the radius is half this, so

Substitute in the surface area formula:

### Example Question #3 : How To Find The Surface Area Of A Cone

The radius of the base of a cone is ; its slant height is two-thirds of the diameter of that base. Give its surface area in terms of .

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone with base of radius and slant height is

.

The diameter of the base is twice radius , or , and its slant height is two-thirds of this diameter, which is . Substitute this for in the formula:

### Example Question #4 : How To Find The Surface Area Of A Cone

The radius of the base of a cone is ; its height is twice of the diameter of that base. Give its surface area in terms of .

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone with base of radius and slant height is

.

The base has radius and diameter . The height is twice the diamter, which is . Its slant height can be calculated using the Pythagorean Theorem:

Substitute for in the surface area formula:

### Example Question #3 : How To Find The Surface Area Of A Cone

The height of a cone is ; the diameter of its base is twice the height. Give its surface area in terms of .

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone with base of radius and slant height is

.

The diameter of the base is twice the height, which is ; the radius is half this, which is .

The slant height can be calculated using the Pythagorean Theorem:

Substitute for and for in the surface area formula:

### Example Question #6 : How To Find The Surface Area Of A Cone

The circumference of the base of a cone is 80; the slant height of the cone is equal to twice the diameter of the base. Give the surface area of the cone (nearest whole number).

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone with base of radius and slant height is

.

The slant height is twice the diameter, or, equivalently, four times the radius, so

and

The radius of the base is the circumference divided by , which is

Substitute:

### Example Question #7 : How To Find The Surface Area Of A Cone

The circumference of the base of a cone is 100; the height of the cone is equal to the diameter of the base. Give the surface area of the cone (nearest whole number).

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone with base of radius and slant height is

.

The diameter of the base is the circumference divided by , which is

This is also the height .

The radius is half this, or

The slant height can be found by way of the Pythagorean Theorem:

Substitute in the surface area formula:

### Example Question #1 : Cones

A heat shield on a particular satellite takes the form of a cone. If the surface area of the "face" of the cone (not counting the disk on the bottom) is , and the stripe of reflective paint from the tip of the cone is down to the base is feet long, what is the diameter of the disk in feet? Round to 3 significant digits. Round your final answer to the nearest foot.

**Possible Answers:**

**Correct answer:**

In this problem, we only need to consider the part of the formula for conic surface area that deals with slant height, since that is all the information we have.

We know the formula for the lateral surface area of a cone is , and we know that is feet. Plugging in our other values gives us:

Simplify:

Thus, if our radius is approximately feet, our diameter is approximately feet.

### Example Question #9 : How To Find The Surface Area Of A Cone

What is the surface area in square units of a cone with radius units and height units?

**Possible Answers:**

**Correct answer:**

The formula for surface area of a cone is:

, where is the slant height. Since we know the radius, we can calculate the first part without issue:

The second part requires us to calculate slant height. Since all cones have a right angle created by the base and height perpendicular to the base, we can use the Pythagorean theorem to calculate :

Now, we can complete our formula. Don't forget to add in the circular base.

Thus, our surface area is square units.