GMAT Math : Calculating the slope of a line

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #81 : Lines

What is the slope of the line \(\displaystyle Ax + 2Ay = 3A\) ?

Possible Answers:

\(\displaystyle -\frac{2}{A}\)

\(\displaystyle -2\)

\(\displaystyle -\frac{A}{2}\)

\(\displaystyle \frac{A}{2}\)

\(\displaystyle -\frac{1}{2}\)

Correct answer:

\(\displaystyle -\frac{1}{2}\)

Explanation:

Rewrite this equation in slope-intercept form: \(\displaystyle y = mx + b\), where \(\displaystyle m\) is the slope.

\(\displaystyle Ax + 2Ay = 3A\)

\(\displaystyle 2Ay = - Ax + 3A\)

\(\displaystyle \frac{2Ay}{2A} = \frac{- Ax + 3A}{2A}\)

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

The slope is the coefficient of \(\displaystyle x\), which is \(\displaystyle -\frac{1}{2}\).

Example Question #82 : Lines

Give the slope of the line of the equation: \(\displaystyle 0.4x - 0.5y = 20\)

Possible Answers:

\(\displaystyle \frac{4}{5}\)

\(\displaystyle -2\)

\(\displaystyle -\frac{5}{4}\)

\(\displaystyle -\frac{4}{5}\)

\(\displaystyle \frac{5}{4}\)

Correct answer:

\(\displaystyle \frac{4}{5}\)

Explanation:

Rewrite in the slope-intercept form \(\displaystyle y = mx + b\):

\(\displaystyle 0.4x - 0.5y = 20\)

\(\displaystyle \left (0.4x - 0.5y \right )\cdot 10 = 20 \cdot 10\)

\(\displaystyle \left (0.4x \right )\cdot 10-\left ( 0.5y \right )\cdot 10 = 200\)

\(\displaystyle 4x-5y = 200\)

\(\displaystyle 4x-4x-5y = 200-4x\)

\(\displaystyle -5y = -4x+ 200\)

\(\displaystyle -5y \div (-5)=\left ( -4x+ 200 \right )\div (-5)\)

\(\displaystyle y=\left ( -4x \right ) \div (-5)+\left ( 200 \right ) \div (-5)\)

\(\displaystyle y= \frac{4}{5}x-40\)

The slope is the coefficient of \(\displaystyle x\), which is \(\displaystyle \frac{4}{5}\).

Example Question #3 : Calculating The Slope Of A Line

Give the slope of the line of the equation: \(\displaystyle \frac{}{}\)\(\displaystyle \frac{2}{5}x + \frac{6}{7}y = 9\)

Possible Answers:

\(\displaystyle -\frac{15}{7}\)

\(\displaystyle -\frac{7}{15}\)

\(\displaystyle \frac{45}{2}\)

\(\displaystyle \frac{12}{35}\)

\(\displaystyle \frac{21}{2}\)

Correct answer:

\(\displaystyle -\frac{7}{15}\)

Explanation:

Rewrite in the slope-intercept form \(\displaystyle y = mx + b\):

\(\displaystyle \frac{2}{5}x + \frac{6}{7}y = 9\)

\(\displaystyle \frac{2}{5}x - \frac{2}{5}x + \frac{6}{7}y = - \frac{2}{5}x+ 9\)

\(\displaystyle \frac{6}{7}y = - \frac{2}{5}x+ 9\)

\(\displaystyle \frac{6}{7}y \cdot \frac{7}{6}=\left ( - \frac{2}{5}x+ 9 \right )\cdot \frac{7}{6}\)

\(\displaystyle y=- \frac{2}{5}\cdot \frac{7}{6}x+ 9 \cdot \frac{7}{6}\)

\(\displaystyle y=-\frac{7}{15}x+ \frac{21}{2}\)

The slope is the coefficient of \(\displaystyle x\), which is \(\displaystyle -\frac{7}{15}\)

Example Question #4 : Calculating The Slope Of A Line

Give the slope of the line of the equation

\(\displaystyle 5y = x - 7\)

Possible Answers:

\(\displaystyle \frac{1}{5}\)

\(\displaystyle 5\)

\(\displaystyle -\frac{7}{5}\)

\(\displaystyle \frac{7}{5}\)

\(\displaystyle -\frac{1}{5}\)

Correct answer:

\(\displaystyle \frac{1}{5}\)

Explanation:

Rewrite in the slope-intercept form \(\displaystyle y = mx + b\):

\(\displaystyle 5y = x - 7\)

\(\displaystyle \frac{1}{5} \cdot 5y = \frac{1}{5} \cdot \left ( x - 7 \right )\)

\(\displaystyle y = \frac{1}{5} x - \frac{7}{5} \right )\)

The slope is the coefficient of \(\displaystyle x\), or \(\displaystyle \frac{1}{5}\).

Example Question #5 : Calculating The Slope Of A Line

What is the slope of the line that contains \(\displaystyle (1,4)\) and \(\displaystyle (7,10)\)?

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle \frac{2}{3}\)

\(\displaystyle \frac{14}{8}\)

\(\displaystyle \frac{3}{2}\)

Correct answer:

\(\displaystyle 1\)

Explanation:

The slope formula is:

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

\(\displaystyle (1,4)\ and\ (7,10)\)

\(\displaystyle m= \frac{7-1}{10-4}\)

\(\displaystyle m= \frac{6}{}6\)

\(\displaystyle m=1\)

Example Question #6 : Calculating The Slope Of A Line

What is the slope of the line that contains \(\displaystyle (1,2)\) and \(\displaystyle (5,2)\)?

Possible Answers:

\(\displaystyle 0\)

\(\displaystyle \frac{1}{4}\)

\(\displaystyle \frac{6}{4}\)

\(\displaystyle \frac{4}{6}\)

Correct answer:

\(\displaystyle 0\)

Explanation:

The slope formula is:

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

\(\displaystyle (1,2)\ and\ (5,2)\)

\(\displaystyle m=\frac{2-2}{5-1}\)

\(\displaystyle m=\frac{0}{4}\)

\(\displaystyle m=0\)

Example Question #7 : Calculating The Slope Of A Line

What is the slope of the line that contains \(\displaystyle (-2,-1)\) and \(\displaystyle (-8,7)\)?

Possible Answers:

\(\displaystyle \frac{4}{3}\)

\(\displaystyle -\frac{4}{3}\)

\(\displaystyle -\frac{3}{4}\)

\(\displaystyle \frac{3}{4}\)

Correct answer:

\(\displaystyle -\frac{4}{3}\)

Explanation:

The slope formula is:

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

\(\displaystyle (-2,-1)\ and\ (-8,7)\)

\(\displaystyle m=\frac{7-(-1)}{-8-(-2)}\)

\(\displaystyle m=\frac{7+1}{-8+2}\)

\(\displaystyle m=\frac{8}{-6}\)

\(\displaystyle m=-\frac{4}{3}\)

Example Question #21 : Other Lines

A iine goes through points \(\displaystyle (6,N + 4 )\) and \(\displaystyle (3,2N + 6)\). What is its slope?

Possible Answers:

\(\displaystyle \frac{3}{N-2}\)

\(\displaystyle \frac{N+2}{3}\)

\(\displaystyle \frac{-N-2}{3}\)

\(\displaystyle \frac{N-2}{3}\)

\(\displaystyle \frac{3}{N+2}\)

Correct answer:

\(\displaystyle \frac{-N-2}{3}\)

Explanation:

Substitute \(\displaystyle x_1= 6 , y_1=N + 4,x_2= 3, y_2 =2N + 6\) in the slope formula:

\(\displaystyle m = \frac{y_2-y_1}{x_2-x_1}\)

\(\displaystyle m = \frac{(2N+6 )- (N+4)}{3-6} = \frac{2N+6 -N-4}{-3}= \frac{N+2}{-3} = \frac{-N-2}{3}\)

Example Question #1 : Calculating The Slope Of A Line

In the \(\displaystyle xy\)-plane, what is the slope of the line with equation 4x+5y=8\(\displaystyle 4x+5y=8\) ?

Possible Answers:

-\frac{4}{5}\(\displaystyle -\frac{4}{5}\)

\frac{1}{2}\(\displaystyle \frac{1}{2}\)

\frac{8}{5}\(\displaystyle \frac{8}{5}\)

-4\(\displaystyle -4\)

4\(\displaystyle 4\)

Correct answer:

-\frac{4}{5}\(\displaystyle -\frac{4}{5}\)

Explanation:

Put the equation in slope-intercept form to solve for the slope:

y=mx+b\(\displaystyle y=mx+b\), where m is the slope and b is the intercept

Rearrange terms: 5y=-4x+8\(\displaystyle 5y=-4x+8\)

Divide by 5: y=-\frac{4}{5}x+\frac{8}{5}\(\displaystyle y=-\frac{4}{5}x+\frac{8}{5}\)

slope = -\frac{4}{5}\(\displaystyle -\frac{4}{5}\)

Example Question #10 : Calculating The Slope Of A Line

Give the slope of the line with the equation \(\displaystyle \frac{4}{3} x = \frac{2}{5} y - 10\).

Possible Answers:

\(\displaystyle \frac{1}{25}\)

\(\displaystyle \frac{15}{8}\)

\(\displaystyle \frac{8}{15}\)

\(\displaystyle \frac{10}{3}\)

\(\displaystyle \frac{3}{10}\)

Correct answer:

\(\displaystyle \frac{10}{3}\)

Explanation:

Rewrite in slope-intercept form:

\(\displaystyle \frac{4}{3} x = \frac{2}{5} y - 10\)

\(\displaystyle \frac{4}{3} x + 10 = \frac{2}{5} y - 10 + 10\)

\(\displaystyle \frac{2}{5} y = \frac{4}{3} x + 10\)

\(\displaystyle \frac{5} {2} \cdot \frac{2}{5} y= \frac{5} {2} \cdot \left ( \frac{4}{3} x + 10 \right )\)

\(\displaystyle y= \frac{5} {2} \cdot \frac{4}{3} x + \frac{5} {2} \cdot 10\)

\(\displaystyle y= \frac{10}{3} x +25\)

The slope is the coefficient of \(\displaystyle x\), which is \(\displaystyle \frac{10}{3}\).

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