ACT Math : Algebra

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : Expressions

The following table shows the temperature of a cup of coffee at different times

Time                           1:09    1:11    1:13    1:15    1:17   

Temperature (ºF)            187.1  184.4  181.7  179.0  176.3

If this trend continues, what will the temperature of the coffee at minute 1:25?

Possible Answers:

168.3°F

162.9°F

160.2°F

171.0°F

165.5°F

Correct answer:

165.5°F

Explanation:

The table shows that for every two minutes, the temperature of the coffee lowers 2.7ºF. At 1:25, 16 minutes, or eight 2-minute intervals have passed, and the temperature of the coffee has lowered by 8*2.7ºF, reaching a temperature of 165.5ºF.

Example Question #1 : Rational Expressions

Amy buys concert tickets for herself and her friends. She initially buys them at $40/ticket. Weeks later, her other friends ask her to buy them tickets, but the prices have increased to $54. Amy buys 7 tickets total and spends $350. How many tickets has she paid $40 on?

Possible Answers:

Correct answer:

Explanation:

Amy has bought 7 tickets, x of them at $40/ticket, and the remaining 7-x at $54/ticket. She spends at total of 

Example Question #1 : How To Evaluate Rational Expressions

What is 

?

Possible Answers:

Correct answer:

Explanation:

To find an equivalency we must rationalize the denominator.

To rationalize the denominator multiply the numerator and denominator by the denominator.

 

  

To simplify completely, factor out a three from the numerator and denominator resulting in the final solution.

 

Example Question #1 : How To Subtract Rational Expressions With Different Denominators

Simplify:

Possible Answers:

Correct answer:

Explanation:

The common denominator of these two fractions simply is the product of the two denominators, namely:

Thus, you will need to multiply each fraction's numerator and denominator by the opposite fraction's denominator:

Let's first simplify the numerator:

, which is the simplest form you will need for this question.

However, the correct answer has the denominator multiplied out. Merely FOIL 

Example Question #911 : Algebra

Simplify:

Possible Answers:

Correct answer:

Explanation:

Always start the simplification of rational expressions with quadratic denominators by factoring the denominator that has a squared element:

Thus, we need to multiply the numerator and denominator of the first term by :

Distribute:

This is simply:

You cannot factor the top in any way that would help you to cancel anything. Therefore, the answer stands as it does. You need to FOIL the denominator back out, as your correct answer is in that form:

Example Question #911 : Algebra

Simplify:

Possible Answers:

Correct answer:

Explanation:

Begin by factoring your denominators:

Therefore, the common denominator of our fractions is:

This will require you to multiply the first fraction by  and the second by . This gives you:

Now, FOIL the second member and distribute the first:

Next, distribute the subtraction:

Finally, simplify:

Example Question #1 : How To Divide Rational Expressions

What is ?

Possible Answers:

Correct answer:

Explanation:

 factors to . Thus, . Canceling out like terms leads to .

Example Question #1 : Rational Expressions

Which of the following is equivalent to \dpi{100} \frac{(\frac{1}{t}-\frac{1}{x})}{x-t} ? Assume that denominators are always nonzero.

Possible Answers:

(xt)^{-1}

t-x

x-t

\frac{x}{t}

x^{2}-t^{2}

Correct answer:

(xt)^{-1}

Explanation:

We will need to simplify the expression \frac{(\frac{1}{t}-\frac{1}{x})}{x-t}. We can think of this as a large fraction with a numerator of \frac{1}{t}-\frac{1}{x} and a denominator of \dpi{100} x-t.

In order to simplify the numerator, we will need to combine the two fractions. When adding or subtracting fractions, we must have a common denominator. \frac{1}{t} has a denominator of \dpi{100} t, and \dpi{100} -\frac{1}{x} has a denominator of \dpi{100} x. The least common denominator that these two fractions have in common is \dpi{100} xt. Thus, we are going to write equivalent fractions with denominators of \dpi{100} xt.

In order to convert the fraction \dpi{100} \frac{1}{t} to a denominator with \dpi{100} xt, we will need to multiply the top and bottom by \dpi{100} x.

\frac{1}{t}=\frac{1\cdot x}{t\cdot x}=\frac{x}{xt}

Similarly, we will multiply the top and bottom of \dpi{100} -\frac{1}{x} by \dpi{100} t.

\frac{1}{x}=\frac{1\cdot t}{x\cdot t}=\frac{t}{xt}

We can now rewrite \frac{1}{t}-\frac{1}{x} as follows:

\frac{1}{t}-\frac{1}{x} = \frac{x}{xt}-\frac{t}{xt}=\frac{x-t}{xt}

Let's go back to the original fraction \frac{(\frac{1}{t}-\frac{1}{x})}{x-t}. We will now rewrite the numerator:

\frac{(\frac{1}{t}-\frac{1}{x})}{x-t} = \frac{\frac{x-t}{xt}}{x-t}

To simplify this further, we can think of \frac{\frac{x-t}{xt}}{x-t} as the same as \frac{x-t}{xt}\div (x-t) . When we divide a fraction by another quantity, this is the same as multiplying the fraction by the reciprocal of that quantity. In other words, a\div b=a\cdot \frac{1}{b}.

 

\frac{x-t}{xt}\div (x-t) = \frac{x-t}{xt}\cdot \frac{1}{x-t}=\frac{x-t}{xt(x-t)}= \frac{1}{xt}

Lastly, we will use the property of exponents which states that, in general, \frac{1}{a}=a^{-1}.

\frac{1}{xt}=(xt)^{-1}

The answer is (xt)^{-1}.

Example Question #1 : Rational Expressions

Simplify:

Possible Answers:

Correct answer:

Explanation:

Multiply by the reciprocal of .

Factor 

Divide by common factors.

Example Question #2 : How To Divide Rational Expressions

Simplify the following expression:

Possible Answers:

Correct answer:

Explanation:

There are a couple ways to go about solving this problem. One could simply take the reciprocal of the second fraction, multiply everything out, and then look for ways to simplify. However, it is almost always easier to simplify before doing any multiplying.

To begin, we need to take the reciprocal of the second fraction, so that our expression becomes:

Then, before we multiply anything out, try to factor out the different parts of this expression. If we have any common factors in the numerator and denominator, we can cancel them out. In this case, the above expression factors as follows:

Conveniently, we can cancel out a bunch of factors here!

The common factors are highlighted in corresponding colors. We can actually cancel everything out here. We have a  in both the numerator and the denominator, and also an  term. We also have two  terms in both the numerator and the denominator, so all of these terms will cancel, and we will be left with :

The reason we can cancel out terms when they are in the numerator and denominator is that we are essentially multiplying and then dividing by the same term. Since multiplication and division are opposite operations, they cancel each other out and we are left with .

Important side note: you can only cancel across two different fractions when you are multiplying and/or dividing. You CANNOT cancel factors across fractions if you are adding or subtracting them.

 

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