GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Understanding Intersecting Lines

Lines

\(\displaystyle \angle FBC\) and which angle form a linear pair?

Possible Answers:

\(\displaystyle \angle EFB\)

There is no angle that forms a linear pair with \(\displaystyle \angle FBC\).

\(\displaystyle \angle FCD\)

\(\displaystyle \angle FB D\)

\(\displaystyle \angle FBA\)

Correct answer:

\(\displaystyle \angle FBA\)

Explanation:

Two angles form a linear pair if they have the same vertex, they share one side, and their interiors do not intersect. \(\displaystyle \angle FBC\) has vertex \(\displaystyle B\) and sides \(\displaystyle \overrightarrow{BF}\) and \(\displaystyle \overrightarrow{BC}\)\(\displaystyle \angle FBA\) has vertex \(\displaystyle B\), shares side \(\displaystyle \overrightarrow{BF}\), and shares no interior points, so this is the correct choice.

Example Question #2 : Understanding Intersecting Lines

Lines

Note: Figure NOT drawn to scale.

Refer to the above diagram. Which is a valid alternative name for \(\displaystyle \overline{AD}\) ?

Possible Answers:

\(\displaystyle \overline{AC}\)

\(\displaystyle \overline{ACD}\)

\(\displaystyle \overline{DBA}\)

\(\displaystyle \overline{DC}\)

\(\displaystyle \overline{DA}\)

Correct answer:

\(\displaystyle \overline{DA}\)

Explanation:

A line segment is named after its two endpoints in either order; \(\displaystyle \overline{AD}\) is the segment with endpoints \(\displaystyle A\) and \(\displaystyle D\), so it can also be named \(\displaystyle \overline{DA}\)

Example Question #3 : Understanding Intersecting Lines

Lines

\(\displaystyle \angle FCB\) and which angle are examples of a pair of vertical angles?

Possible Answers:

\(\displaystyle \angle ECB\)

\(\displaystyle \angle DCF\)

\(\displaystyle \angle DCG\)

There is no angle that forms a vertical pair with \(\displaystyle \angle FCB\).

\(\displaystyle \angle FBC\)

Correct answer:

\(\displaystyle \angle DCG\)

Explanation:

Two angles are vertical if they have the same vertex and if their sides form two pairs of opposite rays. The correct choice will have vertex \(\displaystyle C\), which is the vertex of \(\displaystyle \angle FCB\). Its rays will be the rays opposite \(\displaystyle \overrightarrow{CF }\) and \(\displaystyle \overrightarrow{CB}\), which, are, respectively,  \(\displaystyle \overrightarrow{CG }\) and \(\displaystyle \overrightarrow{CD}\), respectively. The angle that fits this description is \(\displaystyle \angle DCG\)

Example Question #44 : Lines

At what point do \(\displaystyle f(x)\) and \(\displaystyle g(x)\) intersect?

\(\displaystyle \small f(x)=3x+7\)

\(\displaystyle \small \small g(x)=-\frac{1}{3}x+7\)

Possible Answers:

\(\displaystyle (0,-7)\)

\(\displaystyle (-7,0)\)

\(\displaystyle (7,7)\)

\(\displaystyle (0,7)\)

\(\displaystyle (7,0)\)

Correct answer:

\(\displaystyle (0,7)\)

Explanation:

To find where two lines intersect, simply set them equal to each other and solve for \(\displaystyle x\). Then plug the resulting \(\displaystyle x\) value back in to one of the equations and solve for \(\displaystyle y\).

\(\displaystyle \small -\frac{1}{3}+7=3x+7\)

Add \(\displaystyle \frac{1}{3}x\) to both sides and subtract \(\displaystyle 7\) from both sides to isolate our like terms:

\(\displaystyle \small 0=3\frac{1}{3}x\)

So, \(\displaystyle x=0\) must be true for where these lines intersect. Next, plug \(\displaystyle 0\) back in for \(\displaystyle x\) in one of our original equations:

\(\displaystyle \small \small f(x)=3(0)+7=7\)

So, the \(\displaystyle y\) value of our intersection is \(\displaystyle 7\).

This makes the coordinate of our intersection \(\displaystyle (0,7)\).

You can check your answer by plugging in the point you calculated into both equations. Both equations will be true when \(\displaystyle x\) is equal to \(\displaystyle 0\) and \(\displaystyle y\)—in this case, \(\displaystyle f(x)\) and \(\displaystyle g(x)\)—is equal to \(\displaystyle 7\).

Example Question #1 : Polygons

What is the perimeter of a hexagon?

1) Each side measures 10 cm

2) The hexagon is regular.

Possible Answers:

Statement 1 ALONE is sufficient, but Statement 2 alone is not sufficient.

EACH statement ALONE is sufficient.

Statements 1 and 2 TOGETHER are not sufficient.

Statement 2 ALONE is sufficient, but Statement 1 alone is not sufficient.

BOTH statements TOGETHER are sufficient, but neither statement ALONE is sufficient.

Correct answer:

Statement 1 ALONE is sufficient, but Statement 2 alone is not sufficient.

Explanation:

The perimeter is the sum of the measures of the sidelengths.

Knowing that the hexagon is regular only tells you the six sides are congruent; without the measure of any side, this does not help you. 

Knowing only that each of the six sides measures 10 cm is by itself enough to calculate the perimeter to be

\(\displaystyle 6\times 10=60\ cm\).

The answer is that Statement 1 is sufficient, but not Statement 2.

Example Question #671 : Gmat Quantitative Reasoning

Figure

Note: Figure NOT drawn to scale

What is the perimeter of the above figure?

Assume all angles shown in the figure are right angles.

Possible Answers:

\(\displaystyle 70\textrm{ ft}\)

\(\displaystyle 98\textrm{ ft}\)

\(\displaystyle 35\textrm{ ft}\)

\(\displaystyle 43\textrm{ ft}\)

Not enough information is given to answer the question.

Correct answer:

\(\displaystyle 70\textrm{ ft}\)

Explanation:

This figure can be seen as a smaller rectangle cut out of a larger one; refer to the diagram below.

Figure

We can fill in the missing sidelengths using the fact that a rectangle has congruent opposite sides. Once this is done, we can add the lengths of the sides to get the perimeter:

\(\displaystyle P = 10 + 3 + 15 + 7 + 25 + 10 = 70\) feet.

Example Question #2 : Calculating The Perimeter Of A Polygon

What is the perimeter of a rectangle with a length of \(\displaystyle 20cm\) and a width of \(\displaystyle 5cm\)?

Possible Answers:

\(\displaystyle 40cm\)

\(\displaystyle 50cm\)

\(\displaystyle 25cm^{2}\)

\(\displaystyle 25cm\)

\(\displaystyle 50cm^{2}\)

Correct answer:

\(\displaystyle 50cm\)

Explanation:

The perimeter \(\displaystyle P\) of any figure is the sum of the lengths of its sides. Since we have a rectangle with a length of \(\displaystyle 20cm\) and a width of \(\displaystyle 5cm\), we know that there will be two sides of length \(\displaystyle 20cm\) and two sides of width \(\displaystyle 5cm\). Therefore:

\(\displaystyle P=20cm+20cm+5cm+5cm\)

\(\displaystyle P=40cm+10cm\)

\(\displaystyle P=50cm\)

Example Question #4 : Polygons

What is the perimeter of a right triangle with a base of \(\displaystyle 5cm\) and a height of \(\displaystyle 12cm\)?

Possible Answers:

\(\displaystyle 30cm\)

\(\displaystyle 17cm\)

Not enough information provided

\(\displaystyle 13cm\)

\(\displaystyle 60cm\)

Correct answer:

\(\displaystyle 30cm\)

Explanation:

In order to find the perimeter \(\displaystyle P\) of the right triangle, we need to know the lengths of each of its sides. While we are given two sides - the base \(\displaystyle (a)\) and the height \(\displaystyle (b)\) - we do not know the hypotenuse \(\displaystyle (c)\). There are two ways that we can find \(\displaystyle c\), the first of which is the direct application of the Pythagorean Theorem: 

\(\displaystyle a^{2}+b^{2}=c^{2}\)

\(\displaystyle 5^{2}+12^{2}=c^{2}\)

\(\displaystyle 25+144=c^{2}\)

\(\displaystyle 13=c\)

We could have also noted that \(\displaystyle 5:12:13\) is a common Pythagorean Triple and deduced the value of \(\displaystyle c\) that way.

Now that we have all three side lengths, we can calculate \(\displaystyle P\):

\(\displaystyle P=5cm+12cm+13cm\)

\(\displaystyle P=30cm\)

 

 

 

Example Question #5 : Polygons

What is the perimeter of an octagon with equal side lengths of \(\displaystyle 15cm\) each?

Possible Answers:

\(\displaystyle 105cm\)

\(\displaystyle 120cm\)

\(\displaystyle 90cm\)

\(\displaystyle 60cm\)

\(\displaystyle 45cm\)

Correct answer:

\(\displaystyle 120cm\)

Explanation:

Starting with the knowledge that we are dealing with an octagon, an 8-sided figure, we calculate the perimeter \(\displaystyle P\) by adding the lengths of all 8 sides. Since we also know that each side measures \(\displaystyle 15cm\), we can use multiplication:

\(\displaystyle P=8\times15cm\)

\(\displaystyle P=120cm\)

 

 

Example Question #1 : Polygons

\(\displaystyle \textup{QWERT}\) is a pentagon with two sets of congruent sides and one side that is longer than all the others.

The smallest pair of congruent sides are 5 inches long each.

The other two congruent sides are 1.5 times bigger than the smallest sides.

The last side is twice the length of the smallest sides.

What is the perimeter of \(\displaystyle \textup{QWERT}\)?

Possible Answers:

\(\displaystyle 30\ \textup{meters}\)

\(\displaystyle 35\ \textup{meters}\)

\(\displaystyle 45\ \textup{meters}\)

\(\displaystyle 40\ \textup{meters}\)

\(\displaystyle 50\ \textup{meters}\)

Correct answer:

\(\displaystyle 35\ \textup{meters}\)

Explanation:

A pentagon is a 5 sided shape. We are given that two sides are 5 inches each.

Side 1 = 5inches

Side 2 = 5 inches

The next two sides are each 1.5 times bigger than the smallest two sides.

\(\displaystyle \small 5*1.5=7.5\)

Side 3 =Side 4= 7.5 inches

The last side is twice the size of the smallest side, 

Side 5 =10 inches

Add them all up for our perimeter:

5+5+7.5+7.5+10=35 inches long

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