ACT Math : How to find the solution to a rational equation with LCD

Study concepts, example questions & explanations for ACT Math

varsity tutors app store varsity tutors android store varsity tutors ibooks store

Example Questions

Example Question #121 : Linear / Rational / Variable Equations

John, Jill, and Jack are splitting a pizza. John eats \(\displaystyle 1/2\) of the pizza and Jill eats \(\displaystyle 1/3\) of the pizza. How much of the pizza is left for Jack?

Possible Answers:

\(\displaystyle 1/3\)

\(\displaystyle None\)

\(\displaystyle 1/6\)

\(\displaystyle 1/5\)

\(\displaystyle 3/5\)

Correct answer:

\(\displaystyle 1/6\)

Explanation:

We can write an equation for the amount of pizza eaten, with \(\displaystyle x\) as the amount left for Jack.

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

To solve this equation, we must find the lowest common denominator of \(\displaystyle 1/2\) and \(\displaystyle 1/3\). We can list the multiples of \(\displaystyle 2\) and \(\displaystyle 3\) to find the least common multiple:

\(\displaystyle 2: 2, 4, 6, 8, 10, 12, ...\)

\(\displaystyle 3: 3, 6, 12, 15, 18, 21, ...\)

We can see that the least common multiple of \(\displaystyle 2\) and \(\displaystyle 3\) is \(\displaystyle 6\), so we can rewrite each of the fractions with a denominator of \(\displaystyle 6\).

\(\displaystyle \frac{1}{2}\cdot \frac{3}{3} = \frac{3}{6}\)

\(\displaystyle \frac{1}{3}\cdot \frac{2}{2} = \frac{2}{6}\)

When we put these fractions back into the equation, we can solve for \(\displaystyle x\):

\(\displaystyle \frac{3}{6} + \frac{2}{6} + x = 1\)

\(\displaystyle \frac{5}{6} + x = 1\)

\(\displaystyle x = \frac{1}{6}\)

Example Question #121 : Equations / Inequalities

What is the slope of a line represented by the equation:

\(\displaystyle 15y + 3x = 4\)

Possible Answers:

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

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

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

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

Correct answer:

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

Explanation:

To solve problems where you need to find the slope of a line in a given equation, change the equation so that it matches y-intercept form:

\(\displaystyle y=mx+b\)

For this equation, first move the 3x over to the other side of the equation.

\(\displaystyle 15y + 3x = 4\)

         \(\displaystyle -3x\)   \(\displaystyle -3x\)

The equation should now look like this:

\(\displaystyle 15y = -3x + 4\)

Then, divide by 15 to isolate the variable \(\displaystyle y\).

\(\displaystyle \frac{15y}{15} =-\frac{3x}{15} + \frac{4}{15} \rightarrow y =-\frac{3}{15}x + \frac{4}{15}\)

Then simplify

\(\displaystyle y =-\frac{3}{15}x + \frac{4}{15} \rightarrow y =-\frac{1}{5}x + \frac{4}{15}\)

Whatever number is before the x in the equation (m) is your slope.

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

Example Question #121 : Equations / Inequalities

 Rational_5

Possible Answers:

–2

–1

2

0

1

Correct answer:

2

Explanation:

Rational_2

Rational_3

Rational_4

Example Question #1 : How To Find The Solution To A Rational Equation With Lcd

Linesmb1

Possible Answers:

b/(m– 1)

bm/(m+ 1)

–bm/(m+ 1)

b/(m+ 1)

–b/(+ 1)

Correct answer:

b/(m+ 1)

Explanation:

Linesmb5

Linesmb4

Example Question #1 : How To Find The Solution To A Rational Equation With Lcd

In the equation below, \(\displaystyle m\), \(\displaystyle p\), and \(\displaystyle k\) are non-zero numbers. What is the value of \(\displaystyle m\) in terms of \(\displaystyle p\) and \(\displaystyle k\)?

\(\displaystyle \frac{1}{m^3}-\frac{1}{k^2}=\frac{1}{p}\)

Possible Answers:

\(\displaystyle m=p^{\frac{1}{2}}-k^{\frac{1}{3}}\)

\(\displaystyle m=(\frac{p+k^2}{pk^2})^{\frac{1}{3}}\)

\(\displaystyle m=\frac{p^2k^3}{p+k^2}\)

\(\displaystyle m=(\frac{p+k^2}{2})^3\)

\(\displaystyle m=(\frac{pk^2}{p+k^2})^{\frac{1}{3}}\)

Correct answer:

\(\displaystyle m=(\frac{pk^2}{p+k^2})^{\frac{1}{3}}\)

Explanation:

Pkm_7-21-13

Pkm2_7-21-13

Learning Tools by Varsity Tutors