GRE Math : Geometry

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #301 : Geometry

Quantity A: 

The -intercept of the line 

Quantity B: 

The -intercept of the line 

Possible Answers:

The relationship cannot be determined from the information given. 

Quantity B is greater

Quantity A is greater

The two quantities are equal.

Correct answer:

The two quantities are equal.

Explanation:

The key to these quantitative comparison problems is to figure out the worth of both quantities, or figure out whether evaluating the quantities is even possible.  In this case, evaluating the quantities is a fairly straightforward case of figuring out the intercepts of two different lines, which is possible.  Therefore, you can already discount "the relationship cannot be determined from the information given".

To solve quantity A:  is in  form, where  is the -intercept. Therefore, the -intercept is equal to

To solve quantity B: , you have to sole for the  intercept.  The quickest way to figure out the answer is to remember that the  axis exists at the line , therefore to find out where the line crosses the  axis, you can set  and solve for .  

 

-3.5 = .5x - 1.5

Both quantity A and quantity B , therefore the two quantities are equal.

 

 

Example Question #1 : X And Y Intercept

What is the -intercept of the following equation? 

Possible Answers:

Correct answer:

Explanation:

To find the -intercept, you must plug  in for .  

This leaves you with 

.  

Then you must get you by itself so you add  to both sides 

.  

Then divide both sides by  to get 

.  

For the coordinate point,  goes first then  and the answer is .

Example Question #1 : How To Find The Equation Of A Curve

What is the slope of the line whose equation is \dpi{100} \small 8x+12y=20?

Possible Answers:

\dpi{100} \small 2

\dpi{100} \small -\frac{2}{3}

\dpi{100} \small \frac{2}{3}

\dpi{100} \small -\frac{3}{2}

\dpi{100} \small \frac{3}{2}

Correct answer:

\dpi{100} \small -\frac{2}{3}

Explanation:

Solve for \dpi{100} \small y so that the equation resembles the \dpi{100} \small y=mx+b form. This equation becomes \dpi{100} \small -\frac{2}{3}x+\frac{5}{3}. In this form, the \dpi{100} \small m is the slope, which is \dpi{100} \small -\frac{2}{3}.

Example Question #2 : X And Y Intercept

Which of the following equations has a -intercept of ?

Possible Answers:

Correct answer:

Explanation:

To find the -intercept, you need to find the value of the equation where .  The easiest way to do this is to substitute in  for your value of  and see where you get  for .  If you do this for each of your equations proposed as potential answers, you find that  is the answer.

Substitute in  for :

Example Question #3 : X And Y Intercept

If  is a line that has a -intercept of  and an -intercept of , which of the following is the equation of a line that is perpendicular to ?

Possible Answers:

Correct answer:

Explanation:

If  has a -intercept of , then it must pass through the point .

If its -intercept is , then it must through the point .

The slope of this line is .

Therefore, any line perpendicular to this line must have a slope equal to the negative reciprocal, which is . Only  has a slope of .

Example Question #1 : Solid Geometry

The area of the base of a circular right cylinder is quadrupled. By what percentage is the outer face increased by this change?

Possible Answers:

100%

300%

200%

250%

400%

Correct answer:

100%

Explanation:

The base of the original cylinder would have been πr2, and the outer face would have been 2πrh, where h is the height of the cylinder.

Let's represent the original area with A, the original radius with r, and the new radius with R: therefore, we know πR2 = 4A, or πR24πr2. Solving for R, we get R = 2r; therefore, the new outer face of the cylinder will have an area of 2πRh or 2π2rh or 4πrh, which is double the original face area; thus the percentage of increase is 100%. (Don't be tricked into thinking it is 200%. That is not the percentage of increase.)

Example Question #305 : Geometry

What is the surface area of a cylinder with a radius of 17 and a height of 3?

Possible Answers:

3107

1984

2000

2137

2205

Correct answer:

2137

Explanation:

We need the formula for the surface area of a cylinder: SA = 2πr2 + 2πrh. This formula has π in it, but the answer choices don't. This means we must approximate π. None of the answers are too close to each other so we could really even use 3 here, but it is safest to use 3.14 as an approximate value of π.

Then SA = 2 * 3.14 * 172 + 2 * 3.14 * 17 * 3 ≈ 2137

Example Question #1501 : Gre Quantitative Reasoning

What is the surface area of a cylinder with a radius of 6 and a height of 9?

Possible Answers:

96π

64π

180π

108π

225π

Correct answer:

180π

Explanation:

surface area of a cylinder

= 2πr2 + 2πrh

= 2π * 62 + 2π * 6 *9

= 180π

Example Question #306 : Geometry

Quantitative Comparison

Quantity A: The volume of a cylinder with a radius of 3 and a height of 4

Quantity B: 3 times the volume of a cone with a radius of 3 and a height of 4

Possible Answers:

The two quantities are equal.

Quantity A is greater.

The relationship cannot be determined from the information given.

Quantity B is greater.

Correct answer:

The two quantities are equal.

Explanation:

There is no need to do the actual computations here to find the two volumes. The volume of a cone is exactly 1/3 the volume of a cylinder with the same height and radius. That means the two quantities are equal. The formulas show this relationship as well: volume of a cone = πr2h/3 and volume of a cylinder = πr2h

Example Question #2 : Solid Geometry

A right circular cylinder of volume  has a height of 8.

Quantity A: 10

Quantity B: The circumference of the base

Possible Answers:

The two quantities are equal

The relationship cannot be determined from the information provided.

Quantity A is greater

Quantity B is greater

Correct answer:

Quantity B is greater

Explanation:

The volume of any solid figure is . In this case, the volume of the cylinder is  and its height is , which means that the area of its base must be . Working backwards, you can figure out that the radius of a circle of area  is . The circumference of a circle with a radius of  is , which is greater than .

 

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