GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #61 : Coordinate Geometry

 has as its graph a vertical parabola on the coordinate plane. You are given that , but you are given neither  nor .

Which of the following can you determine without knowing the values of  and  ?

I) Whether the curve opens upward or opens downward

II) The location of the vertex

III) The location of the -intercept

IV) The locations of the -intercepts, if there are any

V) The equation of the line of symmetry

Possible Answers:

II and V only

III only

I only

V only

III and IV only

Correct answer:

I only

Explanation:

I) The orientation of the parabola is determined solely by the value of . Since , the parabola can be determined to open upward.

II and V) The -coordinate of the vertex is ; since you are not given , you cannot find this. Also, since the line of symmetry has equation , for the same reason, you cannot find this either.

III) The -intercept is the point at which ; by substitution, it can be found to be at  is unknown, so the -intercept cannot be found.

IV) The -intercept(s), if any, are the point(s) at which . This is solvable using the quadratic formula

Since all three of  and  must be known for this to be evaluated, and only  is known, the -intercept(s) cannot be identified.

The correct response is I only.

Example Question #1 : How To Graph A Quadratic Function

The parabolas of the functions  and  on the coordinate plane have the same vertex.

If we define , which of the following is a possible equation for  ?

Screen shot 2016 02 10 at 12.25.12 pm

Possible Answers:

None of the other responses gives a correct answer.

Correct answer:

Explanation:

The eqiatopm of  is given in the vertex form

,

so the vertex of its parabola is . The graphs of  and  are parabolas with the same vertex, so they must have the same values for  and 

For the function ,  and .

Screen shot 2016 02 10 at 12.25.12 pm

Of the five choices, the only equation of   that has these same values, and that therefore has a parabola with the same vertex, is .

Screen shot 2016 02 10 at 12.27.19 pm

To verify, graph both functions on the same grid.

Screen shot 2016 02 10 at 12.28.14 pm

Example Question #1 : Graphing A Line

A line has slope . Which of the following could be its - and -intercepts, respectively?

Possible Answers:

 and 

 and 

None of the other responses gives a correct answer.

 and 

 and 

Correct answer:

None of the other responses gives a correct answer.

Explanation:

Let  and  be the - and -intercepts, respectively, of the line. Then the slope of the line is , or, equilvalently, 

We do not need to find the actual slopes of the four choices if we observe that in each case,  and  are of the same sign. Since the quotient of two numbers of the same sign is positive, it follows that  is negative, and therefore, none of the pairs of intercepts can be those of a line with positive slope .

Example Question #2 : Graphing A Line

A line has slope . Which of the following could be its - and -intercepts, respectively?

Possible Answers:

 and 

 and 

 and :

None of the other responses gives a correct answer.

 and 

Correct answer:

 and 

Explanation:

 Let  and  be the - and -intercepts, respectively, of the line. Then the slope of the line is , or, equilvalently, 

 

We can examine the intercepts in each choice to determine which set meets these conditions.

 and :

Slope: 

 

 and 

Slope: 

 

 and 

Slope: 

 

 and 

Slope: 

 

 and  comprise the correct choice.

 

Example Question #1011 : Gmat Quantitative Reasoning

Line_1

Which of the following equations can be graphed with a line perpendicular to the green line in the above figure, and with the same -intercept?

Possible Answers:

Correct answer:

Explanation:

The slope of the green line can be calculated by noting that the - and -intercepts of the line are, respectively,  and .  If  and  be the - and -intercepts, respectively, of a line, the slope of the line is . This makes the slope of the green line 

Any line perpendicular to this line must have as its slope the opposite reciprocal of this, or . Since the desired line must also have -intercept , the equation of the line, in point=slope form, is

which can be simplified as

Example Question #4 : Graphing A Line

A line passes through the vertex and the -intercept of the parabola of the equation . What is the equation of the line?

Possible Answers:

Correct answer:

Explanation:

To locate the -intercept of the equation , substitute 0 for :

The -intercept of the parabola is .

The vertex of the parabola of an equation of the form  has -coordinate . Here, we substitute , to obtain -coordinate

.

To find the -coordinate, substitute this for :

The vertex is .

The line includes points  and ; apply the slope formula:

The slope is , and the -intercept is ; in the slope-intercept form , substitute for  and . The equation of the line is .

Example Question #5 : Graphing A Line

Give the equation of a line with undefined slope that passes through the vertex of the graph of the equation .

Possible Answers:

Correct answer:

Explanation:

A line with undefined slope is a vertical line, and its equation is  for some , so the -coordinate of all points it passes through is . If it goes through the vertex of a parabola , then the line has the equation . Therefore, all we need to find is the -coordinate of the vertex of the parabola.

The vertex of the parabola of the equation  has as its -coordinate , which, for the parabola of the equation , can be found by setting :

The desired line is .

Example Question #2 : Graphing A Line

A line has slope 4. Which of the following could be its - and -intercepts, respectively?

Possible Answers:

 and 

 and 

None of the other responses gives a correct answer.

 and 

 and 

Correct answer:

 and 

Explanation:

 Let  and  be the - and -intercepts, respectively, of the line. Then the slope of the line is , or, equilvalently, 

 

We can examine the intercepts in each choice to determine which set meets these conditions.

 and 

Slope:  

 

 and 

Slope:  

 

 and 

Slope:  

 

 and 

Slope:  

 

 and  comprise the correct choice, since a line passing through these points has the correct slope.

Example Question #3 : Graphing A Line

The graph of the equation  shares its -intercept and one of its -intercepts with a line of negative slope. Give the equation of that line.

Possible Answers:

Correct answer:

Explanation:

The -intercept of the line coincides with that of the graph of the quadratic equation, which is a parabola; to find the -intercept of the parabola, substitute 0 for  in the quadratic equation:

The -intercept of the parabola, and of the line, is .

The -intercept of the line coincides with one of those of the parabola; to find the -intercepts of the parabola, substitute 0 for  in the equation:

Using the  method, split the middle term by finding two integers whose product is  and whose sum is ; by trial and error we find these to be  and 4, so proceed as follows:

Split:

or

The -intercepts of the parabola are  and , so the -intercept of the line is one of these. We examine both possibilities.

If  and  be the - and -intercepts, respectively, of the line, then the slope of the line is , or, equivalently, 

If the intercepts are  and , the slope is ; if the intercepts are  and , the slope is . Since the line is of negative slope, we choose the line of slope ; since its -intercept is , then we can substitute  in the slope-intercept form of the line, , to get the correct equation, .

Example Question #8 : Graphing A Line

Line_1

Which of the following equations can be graphed with a line parallel to the green line in the above figure?

Possible Answers:

None of the other choices gives a correct answer.

Correct answer:

Explanation:

If  and  be the - and -intercepts, respectively, of a line, the slope of the line is 

The - and -intercepts of the line are, respectively,  and , so , and consequently, the slope of the green line is .  A line parallel to this line must also have slope 

Each of the equations of the lines is in slope-intercept form , where  is the slope, so we need only look at the coefficients of . The only choice that has  as its -coefficient is , so this is the correct choice.

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