GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #2 : Calculating Whether Point Is On A Line With An Equation

Consider segment \(\displaystyle \overline{JK}\) which passes through the points \(\displaystyle \left ( 4,5\right )\) and \(\displaystyle \left ( 144,75\right )\).

If the point \(\displaystyle \left ( 16,y\right )\) is on \(\displaystyle \overline{JK}\), what is the value of y?

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle -5\)

\(\displaystyle 11\)

\(\displaystyle 5\)

\(\displaystyle -11\)

Correct answer:

\(\displaystyle 11\)

Explanation:

First, use the points to find the equation of JK:

Given that JK passes through (4,5) and (144,75) we can find the slope as follows:

Slope is found via:

\(\displaystyle m=\frac{y'-y}{x'-x}\)

Plug in and calculate:

\(\displaystyle \small \small m=\frac{75-5}{144-4}=\frac{70}{140}=\frac{1}{2}\)

Next, we need to use one of our points and the slope to find our y-intercept. I'll use (4,5).

\(\displaystyle \small 5=\frac{1}{2}*4+b\)

\(\displaystyle \small b=5-2=3\)

So our answer is: 

\(\displaystyle \small y=\frac{x}{2}+3\)

To find y, we need to plug in 16 for x and solve:

 

\(\displaystyle \small \small y=\frac{16}{2}+3=8+3=11\)

Example Question #1 : Other Lines

If \(\displaystyle f(x)\) is defined as follows, is the point \(\displaystyle \left ( -2,5\right )\)on \(\displaystyle f(x)\)?

\(\displaystyle \small f(x)=4x+13\)

Possible Answers:

No

Cannot be calculated from the provided information

Yes

f(x) is undefined at (-2,5)

Correct answer:

Yes

Explanation:

To find out if (-2,5) is on f(x), simply plug the point into f(x)

\(\displaystyle \small f(x)=4x+13\)

Becomes,

\(\displaystyle \small \small 5=4*-2+13=-8+13=5\)

So yes, it does!

Example Question #4 : Calculating Whether Point Is On A Line With An Equation

Which of the following are points along \(\displaystyle g(x)\) if

\(\displaystyle {}g(x)=4x^2-8\).

Possible Answers:

\(\displaystyle (3,28)\)

\(\displaystyle (4,64)\)

\(\displaystyle (2,4)\)

\(\displaystyle (-3,-28)\)

\(\displaystyle (3,-28)\)

Correct answer:

\(\displaystyle (3,28)\)

Explanation:

One way to solve this one is by plugging in each of the answer choices and eliminating any that don't work out. Begin with our original g(x)

\(\displaystyle {}g(x)=4x^2-8\)

If we plug in 3 we get

\(\displaystyle {}g(x)=4(3)^2-8=4(9)-8=36-8=28\)

So our point is (3,28).

 

Example Question #71 : Coordinate Geometry

What is the equation of a line with slope \(\displaystyle 1\) and a point \(\displaystyle (1,4)\)?

Possible Answers:

\(\displaystyle y=x+1\)

\(\displaystyle y=x+3\)

\(\displaystyle y=x-4\)

\(\displaystyle y=x+4\)

Correct answer:

\(\displaystyle y=x+3\)

Explanation:

Since the slope and a point on the line are given, we can use the point-slope formula:

\(\displaystyle y-y_{1}=m(x-x_{1})\)

\(\displaystyle m=1\ and\ (1,4)\)

\(\displaystyle y-4=1(x-1)\)

\(\displaystyle y-4=x-1\)

\(\displaystyle y=x-1+4\)

\(\displaystyle y=x+3\)

Example Question #72 : Coordinate Geometry

What is the equation of a line with slope \(\displaystyle 0\) and point \(\displaystyle (5,2)\)?

Possible Answers:

\(\displaystyle y=x+5\)

\(\displaystyle y=5\)

\(\displaystyle y=2\)

\(\displaystyle y=x+2\)

Correct answer:

\(\displaystyle y=2\)

Explanation:

Since the slope and a point on the line are given, we can use the point-slope formula:

\(\displaystyle y-y_{1}=m(x-x_{1})\)

\(\displaystyle m=0\ and\ (5,2)\)

\(\displaystyle y-2=0(x-5)\)

\(\displaystyle y-2=0\)

\(\displaystyle y=2\)

Example Question #3 : Calculating The Equation Of A Line

What is the equation of a line with slope \(\displaystyle -\frac{4}{3}\) and a point \(\displaystyle (-8,7)\)?

Possible Answers:

\(\displaystyle y=-\frac{4}{3}x-\frac{11}{3}\)

\(\displaystyle y=-\frac{4}{3}x-\frac{3}{11}\)

\(\displaystyle y=\frac{4}{3}x+\frac{32}{3}\)

\(\displaystyle y=\frac{4}{3}x+\frac{11}{3}\)

Correct answer:

\(\displaystyle y=-\frac{4}{3}x-\frac{11}{3}\)

Explanation:

Since the slope and a point on the line are given, we can use the point-slope formula:

\(\displaystyle y-y_{1}=m(x-x_{1})\)

slope: \(\displaystyle -\frac{4}{3}\) and point: \(\displaystyle (-8,7)\)

\(\displaystyle y-7=-\frac{4}{3}(x-(-8))\)

\(\displaystyle y-7=-\frac{4}{3}(x+8)\)

\(\displaystyle y-7=-\frac{4}{3}x-\frac{32}{3}\)

\(\displaystyle y=-\frac{4}{3}x-\frac{32}{3}+7\)

\(\displaystyle y=-\frac{4}{3}x-\frac{32}{3}+\frac{21}{3}\)

\(\displaystyle y=-\frac{4}{3}x-\frac{11}{3}\)

Example Question #1 : Calculating The Equation Of A Line

Find the equation of the line through the points \(\displaystyle (4, -2)\) and \(\displaystyle (1, 7)\).

Possible Answers:

\(\displaystyle y=2x-2\)

\(\displaystyle y=3x+3\)

\(\displaystyle y=-3x+10\)

\(\displaystyle y=2x+9\)

\(\displaystyle y=-3\)

Correct answer:

\(\displaystyle y=-3x+10\)

Explanation:

First find the slope of the equation.

m =\frac{rise}{run} =\frac{7 + 2}{1-4} = \frac{9}{-3}=-3\(\displaystyle m =\frac{rise}{run} =\frac{7 + 2}{1-4} = \frac{9}{-3}=-3\)

Now plug in one of the two points to form an equation.  Here we use (4, -2), but either point will produce the same answer.

y-(-2)=-3(x-4)\(\displaystyle y-(-2)=-3(x-4)\)

y + 2=-3x + 12\(\displaystyle y + 2=-3x + 12\)

y=-3x+10\(\displaystyle y=-3x+10\)

Example Question #2 : Calculating The Equation Of A Line

Consider segment \(\displaystyle \overline{JK}\) which passes through the points \(\displaystyle \left ( 4,5\right )\) and \(\displaystyle \left ( 144,75\right )\).

Find the equation of \(\displaystyle \overline{JK}\) in the form \(\displaystyle y=mx+b\).

Possible Answers:

\(\displaystyle \small \small y=2x+3\)

\(\displaystyle \small \small y=\frac{x}{2}+6\)

\(\displaystyle \small y=\frac{x}{2}+3\)

\(\displaystyle \small \small y=-\frac{x}{2}+3\)

\(\displaystyle \small \small y=\frac{x}{2}-3\)

Correct answer:

\(\displaystyle \small y=\frac{x}{2}+3\)

Explanation:

Given that JK passes through (4,5) and (144,75) we can find the slope as follows:

Slope is found via:

\(\displaystyle m=\frac{y'-y}{x'-x}\)

Plug in and calculate:

\(\displaystyle \small \small m=\frac{75-5}{144-4}=\frac{70}{140}=\frac{1}{2}\)

Next, we need to use one of our points and the slope to find our y-intercept. I'll use (4,5).

\(\displaystyle \small 5=\frac{1}{2}*4+b\)

\(\displaystyle \small b=5-2=3\)

So our answer is: 

\(\displaystyle \small y=\frac{x}{2}+3\)

Example Question #6 : Calculating The Equation Of A Line

Determine the equation of a line that has the points \(\displaystyle (-2,3)\) and \(\displaystyle (6,7)\) ?

Possible Answers:

\(\displaystyle y=-2x-2\)

\(\displaystyle y=\frac{1}{2}x+4\)

\(\displaystyle y=-\frac{1}{4}x+2\)

\(\displaystyle y=2x+2\)

\(\displaystyle y=-\frac{1}{2}x-4\)

Correct answer:

\(\displaystyle y=\frac{1}{2}x+4\)

Explanation:

The equation for a line in standard form is written as follows:

\(\displaystyle y=mx+b\)

Where \(\displaystyle m\) is the slope and \(\displaystyle b\) is the y intercept. We start by calculating the slope between the two given points using the following formula:

\(\displaystyle m=\frac{y_2-y_1}{x_2-x_1}=\frac{7-3}{6-(-2)}=\frac{4}{8}=\frac{1}{2}\)

Now we can plug either of the given points into the formula for a line with the calculated slope and solve for the y intercept:

\(\displaystyle y=mx+b\)

\(\displaystyle 3=(\frac{1}{2})(-2)+b\)

\(\displaystyle b=4\)

We now have the slope and the y intercept of the line, which is all we need to write its equation in standard form:

\(\displaystyle y=\frac{1}{2}x+4\)

Example Question #3 : Calculating The Equation Of A Line

Give the equation of the line that passes through the \(\displaystyle y\)-intercept and the vertex of the parabola of the equation

\(\displaystyle y = x^{2} + 5x - 6\).

Possible Answers:

\(\displaystyle y=-x-6\)

\(\displaystyle y = -6x+6\)

\(\displaystyle y=-\frac{5}{2 } x + 6\)

\(\displaystyle y=6x-6\)

\(\displaystyle y=\frac{5}{2 } x - 6\)

Correct answer:

\(\displaystyle y=\frac{5}{2 } x - 6\)

Explanation:

The \(\displaystyle y\)-intercept of the parabola of the equation can be found by substituting 0 for \(\displaystyle x\):

\(\displaystyle y = x^{2} + 5x - 6\)

\(\displaystyle y = 0^{2} + 5 (0) - 6\)

\(\displaystyle y = -6\)

This point is \(\displaystyle (0, -6)\).

The vertex of the parabola of the equation \(\displaystyle y = a x^{2} + bx+c\) has \(\displaystyle x\)-coordinate \(\displaystyle - \frac{b}{2a}\), and its \(\displaystyle y\)-coordinate can be found using substitution for \(\displaystyle x\). Setting \(\displaystyle a = 1\) and \(\displaystyle b= 5\):

\(\displaystyle x = - \frac{b}{2a} = - \frac{5}{2 \cdot 1} = - \frac{5}{2 }\)

\(\displaystyle y = \left ( - \frac{5}{2 } \right )^{2} + 5 \left ( - \frac{5}{2 } \right ) - 6\)

\(\displaystyle y = \frac{25}{4 } - \frac{25}{2 } - 6\)

\(\displaystyle y = \frac{25}{4 } - \frac{50}{4 } - \frac{24}{4}\)

\(\displaystyle y = - \frac{49}{4 }\)

The vertex is \(\displaystyle \left (- \frac{5}{2 },- \frac{49}{4 } \right )\)

The line connects the points \(\displaystyle (0, -6)\) and \(\displaystyle \left (- \frac{5}{2 },- \frac{49}{4 } \right )\). Its slope is

\(\displaystyle m= \frac{y_{2} - y_{1}}{x_{2} - x_{1}}\)

\(\displaystyle = \frac{-6-\left ( - \frac{49}{4 } \right )}{0 - \left (- \frac{5}{2 } \right )}\)

\(\displaystyle = \frac{-\frac{24 }{4 } + \frac{49}{4 } }{ \frac{5}{2 } }\)

\(\displaystyle = \frac{ \frac{25}{4 } }{ \frac{5}{2 } }\)

\(\displaystyle = \frac{25}{4 } \cdot \frac{2 } {5}\)

\(\displaystyle =\frac{5}{2 }\)

Since the line has \(\displaystyle y\)-intercept \(\displaystyle (0, -6)\) and slope \(\displaystyle m =\frac{5}{2 }\), the equation of the line is \(\displaystyle y=\frac{5}{2 } x + (- 6)\), or \(\displaystyle y=\frac{5}{2 } x - 6\).

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