ACT Math : Solid Geometry

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #151 : Solid Geometry

You have an empty cone and a cylinder filled with water. The cone has a diameter of \displaystyle 8 and a height of \displaystyle 9. The cylinder has a diameter of \displaystyle 10 and a height of \displaystyle 12. If you dump the water from the cylinder into the cone until it is filled, what volume of water will remain in the cylinder?

Possible Answers:

\displaystyle 252\pi

\displaystyle 1176\pi

\displaystyle 288\pi

\displaystyle 300\pi

\displaystyle 276\pi

Correct answer:

\displaystyle 252\pi

Explanation:

1. Find the volumes of the cone and cylinder:

Cone:

Since the diameter is \displaystyle 8, the radius is \displaystyle 4.

\displaystyle Volume=\frac{1}{3}\pi r^{2}h

\displaystyle Volume=\frac{1}{3}\pi (4^{2})(9)=48\pi

Cylinder:

Since the diameter is \displaystyle 10, the radius is \displaystyle 5.

\displaystyle Volume=\pi r^{2}h

\displaystyle Volume=\pi (5^{2})(12)=300\pi

 

2. Subtract the cone's volume from the cylinder's volume:

\displaystyle 300\pi-48\pi=252\pi

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

What is the volume of a cone with a height of 7 cm and a radius of 4 cm? Leave your answer in terms of \displaystyle \pi and as a fraction if need be.

Possible Answers:

\displaystyle \frac{448}{3}\pi cm^3

\displaystyle \frac{56}{3} \pi cm^3

\displaystyle \frac{112}{3}\pi cm^3

\displaystyle 112\pi cm^3

\displaystyle \frac{196}{3}\pi cm^3

Correct answer:

\displaystyle \frac{112}{3}\pi cm^3

Explanation:

To find the volume of a cone plug the radius and height into the formula for the volume of a cone.

\displaystyle V = \frac{1}{3}\pi r^2\cdot h

\displaystyle \\=\frac{1}{3}\pi 4^2\cdot 7\\ \\=\frac{112}{3}\pi cm^3

Example Question #152 : Solid Geometry

Which of the following will quadruple the volume of a cone?

  1. Doubling the radius
  2. Doubling the height
  3. Quadrupling the height
Possible Answers:

1, 2 and 3

1 and 3

1 only

3 only

2 only

Correct answer:

1 and 3

Explanation:

Bearing in mind the volume formula for a cone:

\displaystyle V_{cone} = \frac{1}{3}\pi r^2h

Because the volume varies by the square of the radius, doubling the radius will quadruple the volume (since \displaystyle 2^2 = 4.) Because the volume also varies linearly by the height, quadrupling the height will quadruple the volume.

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

What is the volume of a cone with a radius of \displaystyle 6 and a height of \displaystyle 2? Leave your answer in terms of \displaystyle \pi, reduce all fractions.

Possible Answers:

\displaystyle 72\pi

\displaystyle 8\pi

\displaystyle 231.32\pi

\displaystyle 24\pi

\displaystyle 36\pi

Correct answer:

\displaystyle 24\pi

Explanation:

To find the volume of a cone with radius \displaystyle r, and height \displaystyle h use the formula:

\displaystyle V = \frac{1}{3}\pi *r^2*h.

We plug in our given radius and height to find:

\displaystyle V = \frac{1}{3}\pi * 6^2*2 = \frac{72}{3}\pi = 24\pi

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

A conical paper cup is being used as a makeshift funnel for motor oil. If the cup is 100 millimeters deep at the center and has a radius of 70 millimeters, how many cubic millimeters of motor oil can it hold at one time? Round your final answer to the nearest integer.

Possible Answers:

\displaystyle 233333\pi mm^2

\displaystyle 106667\pi mm^2

\displaystyle 99999\pi mm^2

\displaystyle 784333\pi mm^2

\displaystyle 387667\pi mm^2

Correct answer:

\displaystyle 233333\pi mm^2

Explanation:

The formula for the volume of a cone is:

\displaystyle V = \frac{\pi r^2h}{3}

With the information we have, we can simply plug values into this equation and solve.

\displaystyle V = \frac{\pi r^2h}{3} = \frac{(100^2)(70)\pi}{3} \approx 233333\pi

So our cone can hold approximately \displaystyle 233333\pi cubic millimeters of motor oil.

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

Find the volume of a cone whose diameter is \displaystyle 6 and height is \displaystyle 2.

Possible Answers:

\displaystyle 72\pi

\displaystyle 18\pi

\displaystyle 36\pi

\displaystyle 6\pi

\displaystyle 72\pi

Correct answer:

\displaystyle 6\pi

Explanation:

To find the volume of a cone, simply use the following formula. Thus,

\displaystyle V=\frac{1}{3}\pi{r^2}h=\frac{1}{3}*\pi*3^2*2=\frac{1}{3}*9*2*\pi=6\pi

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

Find the volume of a cone with radius \displaystyle 3 and height of \displaystyle 4.

Possible Answers:

\displaystyle 12\pi

\displaystyle 108\pi

\displaystyle 36\pi

\displaystyle 28\pi

Correct answer:

\displaystyle 12\pi

Explanation:

To solve simply use the formula for the voluma of a cone. Thus,

\displaystyle V=\frac{1}{3}\pi{r^2}h=\frac{1}{3}*\pi*3^2*4=12\pi

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

What is the volume of a cone with a radius of 3 mm and a height of 6 mm?

Possible Answers:

Correct answer:

Explanation:

The formula for the volume of a cone is given by the equation:
\displaystyle V = \frac{1}{3} \pi r^2*h.

Pluggin in our values we get:

\displaystyle V = \frac{1}{3} \pi 3^2*6

\displaystyle V=18\pi mm^3

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