ACT Math : Evaluating Expressions

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #31 : Evaluating Expressions

If \(\displaystyle x\ \blacklozenge \ y\) is defined by the formula \(\displaystyle (x^{3}-y)^{2}-x\), what is \(\displaystyle 2\ \blacklozenge \ 1\) equivalent to?

Possible Answers:

\(\displaystyle 49\)

\(\displaystyle 0\)

\(\displaystyle -1\)

\(\displaystyle 34\)

\(\displaystyle 47\)

Correct answer:

\(\displaystyle 47\)

Explanation:

The function \(\displaystyle x\ \blacklozenge \ y\) is defined by \(\displaystyle (x^{3}-y)^{2}-x\). This means that for whatever value is in the space of the \(\displaystyle x\) before the symbol \(\displaystyle \blacklozenge\), in our case 2, is inserted into any \(\displaystyle x\) in the defined function:

\(\displaystyle \dpi{100} (2^{3}-y)^{2}-2\)

For the value that follows \(\displaystyle \blacklozenge\), the \(\displaystyle y\) value of 1 in our case, is inserted into any \(\displaystyle y\) variable in the defined function.

\(\displaystyle \dpi{100} (2^{3}-1)^{2}-2\)

Then simplify:

\(\displaystyle (8-1)^{2}-2\)

\(\displaystyle 7^{2}-2\)

\(\displaystyle 49-2\)

\(\displaystyle 47\)

\(\displaystyle 47\) is our correct answer after all the simplification.

Example Question #32 : Evaluating Expressions

A dress that normally costs $80 before tax is on sale for 15% off. After the discount is subtracted, a 7% sale tax is added. What is the final price of the dress?

Possible Answers:

\(\displaystyle \$50.76\)

\(\displaystyle \$72.00\)

\(\displaystyle \$65.00\)

\(\displaystyle \$72.76\)

Need more information

Correct answer:

\(\displaystyle \$72.76\)

Explanation:

The word problem can be simplified into two steps. First, subtracting the 15% discount:

\(\displaystyle New Price = (Original Price - (Original Price \cdot 0.15))\)

Second, adding the sales tax to the result from the first step:

\(\displaystyle Final Price = (New Price + (New Price \cdot 0.07))\)

The percentage is represented as a decimal by dividing the percentage by 100.

So, for the numbers provided:

New Price = \(\displaystyle (\$80.00-(\$80.00\cdot 0.15))=\$68.00\)

Final Price = \(\displaystyle \$68.00+(\$68.00\cdot 0.07)=\$72.76\)

 

Example Question #2463 : Act Math

Evaluate the expression: 

\(\displaystyle 3(x-2) + y^2-xy\) 

for \(\displaystyle x = 2\) and \(\displaystyle y = -3\)

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 0\)

\(\displaystyle -5\)

\(\displaystyle 15\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 15\)

Explanation:

Plug in the values for the variables and use PEMDAS to dictate the order of the operations. PEMDAS stands for Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction. Using this order of operations we get

 \(\displaystyle (x-2) = 0\) so the first part of the expression is \(\displaystyle 0\).

Next we deal with the exponents,

\(\displaystyle -3^2\)\(\displaystyle =9\).

Then, we deal with the multiplication, 

\(\displaystyle 2\cdot -3 = -6.\) 

Finally, we plug these simplified values back into the equation and solve,

\(\displaystyle 9 - (-6) = 15\).

Example Question #2464 : Act Math

Tickets for a circus show cost \(\displaystyle \$ 5\) each when bought in advance and \(\displaystyle \$7\) each when bought at the door. The circus show's goal is to acquire at least \(\displaystyle \$ 2,000\) in ticket sales. The show group sold \(\displaystyle 153\) opening-night tickets in advance.

What is the minimum number of tickets they need to sell at the door on opening night to reach their goal?

Possible Answers:

\(\displaystyle 200\)

\(\displaystyle 177\)

\(\displaystyle 176\)

\(\displaystyle 293\)

\(\displaystyle 154\)

Correct answer:

\(\displaystyle 177\)

Explanation:

Since \(\displaystyle 153\) tickets were sold in advance, the group earned a revenue of \(\displaystyle 153*\$ 5= \$ 765\). In order to reach their goal of \(\displaystyle \$ 2,000\), they would still need to earn an extra \(\displaystyle (\$ 2000-\$ 765)= \$ 1235.\)

Since each ticket costs \(\displaystyle \$ 7\) at the door, the theatre would need to sell \(\displaystyle \$ 1235/7\)tickets, or \(\displaystyle 177\) tickets (rounded to the next whole number).

Note: the answer is NOT \(\displaystyle 176\) tickets, because if \(\displaystyle 176\) tickets are sold, the revenue would be \(\displaystyle (176*7) + (153*5) = \$ 1997\) , which does not reach the goal of \(\displaystyle \$ 2,000\).

Example Question #2464 : Act Math

If \(\displaystyle x=-4\), what is the value of \(\displaystyle \frac{x^2-1}{x+1}\)?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 15\)

\(\displaystyle 5\)

\(\displaystyle -4\)

\(\displaystyle -5\)

Correct answer:

\(\displaystyle -5\)

Explanation:

Since \(\displaystyle x=-4\) this value can be substituted for \(\displaystyle x\) in the function.

\(\displaystyle \frac{x^2-1}{x+1}}\)

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

\(\displaystyle =\frac{16-1}{-3}\)

Here, the denominator becomes \(\displaystyle -3\), while the numerator becomes \(\displaystyle 15\).

\(\displaystyle =\frac{15}{-3}\)

Hence, 

\(\displaystyle \frac{15}{-3} = -5\).

Example Question #71 : Expressions

If  \(\displaystyle f(x) = 4x^2 + 2x - 4\), then \(\displaystyle f(-2)\) equals?

Possible Answers:

\(\displaystyle 16\)

\(\displaystyle -8\)

\(\displaystyle 36\)

\(\displaystyle -24\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 8\)

Explanation:

When substituting \(\displaystyle (-2)\) for \(\displaystyle x\) in the provided equation, we get

\(\displaystyle 4(-2)^2 +2(-2) -4\),

which can be simplified to

\(\displaystyle 16-4-4\), or \(\displaystyle 8\).

Example Question #33 : Evaluating Expressions

Question 20

In which month has Abraham collected the most stamps?

Possible Answers:

April

May

November

October

July

Correct answer:

May

Explanation:

May corresponds to the month Abraham collected the most stamps, adding 24 to his collection. April, July, October, and November correspond to 18, 6, 21, 12, respectively.

Example Question #73 : Expressions

A company establishes a rewards program such that the bonus received by an employee is given by the model \(\displaystyle b = \frac{s^3}{10}\), where \(\displaystyle s\) is the number of sales an employee completed. If Alex earned $2700 at the end of the month, how many sales has he completed?

Possible Answers:

\(\displaystyle 27\)

\(\displaystyle 90\)

\(\displaystyle 27000\)

\(\displaystyle 30\)

\(\displaystyle 300\)

Correct answer:

\(\displaystyle 30\)

Explanation:

Alex’s bonus of 

\(\displaystyle 2700 = \frac{s^3}{10} \rightarrow 27000 = s^3\rightarrow s = 30.\)

Example Question #34 : Evaluating Expressions

\(\displaystyle 2x + 7 = |-7|\) , then \(\displaystyle x = \:?\)

Possible Answers:

\(\displaystyle -7\)

\(\displaystyle 14\)

\(\displaystyle 0\)

\(\displaystyle 7\)

\(\displaystyle -3.5\)

Correct answer:

\(\displaystyle 0\)

Explanation:

 \(\displaystyle |-7| = 7\). Thus

 \(\displaystyle 2x + 7 = 7\rightarrow 2x = 0 \rightarrow x = 0\)

Example Question #35 : Evaluating Expressions

Evaluate the folling expression given \(\displaystyle x=2\).

\(\displaystyle x^3+\frac{2}{x}-4x^2+x!\)

Possible Answers:

\(\displaystyle -4\)

\(\displaystyle -5\)

\(\displaystyle 8\)

\(\displaystyle 13\)

Correct answer:

\(\displaystyle -5\)

Explanation:

To evaluate, simply plug in \(\displaystyle 2\) for \(\displaystyle x\). Thus:

\(\displaystyle 2^3+\frac{2}{2}-4*2^2+2!=8+1-16+2=-5\)

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