PSAT Math : Algebra

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1083 : Psat Mathematics

Which of the following operations could represent the expression \(\displaystyle 2x^2+7\)?

Possible Answers:

2 times 7 more than the square of x

7 more than the square of 2x

2 times 7 less than the square of x

7 more than 2 times the square of x

7 less than the square of 2x

Correct answer:

7 more than 2 times the square of x

Explanation:

Begin by putting the equation given into your own words. It might sound something similar to:

2 times x squared plus 7

Now, go through each answer choice and see if any of them are similar to this. We immediately see that the answer "7 more than 2 times the square of x" is similar to what we came up with. Let's do a quick run through of the other choices to be sure of our choice: 

"2 times 7 more than the square of x" is equal to \(\displaystyle \small 2(x^2+7)\), which is equivalent to \(\displaystyle \small 2x^2+14\)

"2 times 7 less than the square of x" is equal to \(\displaystyle \small \small 2(x^2-7)\), which is equivalent to \(\displaystyle \small \small 2x^2-14\).

"7 more than the square of 2x" is equal to \(\displaystyle \small (2x)^2+7\), which is equivalent to \(\displaystyle \small 4x^2+7\).

"7 less than the square of 2x" is equal to \(\displaystyle \small \small (2x)^2-7\), which is equivalent to \(\displaystyle \small \small 4x^2-7\).

The only answer that works is "7 more than 2 times the square of x". This is the correct answer.

Example Question #48 : Evaluating And Simplifying Expressions

What does \(\displaystyle (-3(2+3))-4(3(2^2))\) equal?

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 33\)

\(\displaystyle -63\)

\(\displaystyle 19\)

\(\displaystyle -159\)

Correct answer:

\(\displaystyle -63\)

Explanation:

When solving a complex expression, remember the acronym PEMDAS (Parentheses, Exponents, Multiplication, Division, Addition, Subtraction). Reading left to right, begin by doing all operations within the innermost Parentheses first:

\(\displaystyle (-3(2+3))-4(3(2^2))\)

\(\displaystyle =(-3(5))-4(3(4))\)

\(\displaystyle =(-15)-4(12)\)

Continue simplifying using the acronym PEMDAS:

\(\displaystyle =-15-48\)

\(\displaystyle =-63\)

The expression is equal to -63.

Example Question #1 : Rational Expressions

Simplify. 

\(\displaystyle \frac{2x+3}{x+2}+\frac{5x-6}{x+2}\)

Possible Answers:

\(\displaystyle \frac{7x+9}{2x+4}\)

\(\displaystyle \frac{7x-3}{2x+4}\)

\(\displaystyle 5x-1\)

\(\displaystyle \frac{5x-1}{2}\)

\(\displaystyle \frac{7x-3}{x+2}\)

Correct answer:

\(\displaystyle \frac{7x-3}{x+2}\)

Explanation:

\(\displaystyle \frac{2x-3}{x+2}+\frac{5x-6}{x+2}\)

Same denominator means you add straight across the numerators, keeping the denominator the same.

\(\displaystyle \frac{2x-3+5x-6}{x+2}\)

Add like terms. 

\(\displaystyle \frac{2x+5x+3-6}{x+2}\)

Final Answer. 

\(\displaystyle \frac{7x-3}{x+2}\)

Example Question #2 : Rational Expressions

Simplify.

\(\displaystyle \frac{x^{2}-4}{2x+8}+\frac{-12}{2x+8}\)

Possible Answers:

\(\displaystyle \frac{x-2}{6}\)

\(\displaystyle \frac{x^{2}-16}{2x+8}\)

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

\(\displaystyle \frac{x^{2}-16}{x+4}\)

\(\displaystyle \frac{x-4}{2}\)

Correct answer:

\(\displaystyle \frac{x-4}{2}\)

Explanation:

\(\displaystyle \frac{x^{2}-4}{2x+8}+\frac{-12}{2x+8}\)

Check for same Denominator

\(\displaystyle \frac{x^{2}-4+(-12)}{2x+8}\)

Add like terms 

\(\displaystyle \frac{x^{2}-16}{2x+8}\)

Check for GCF or if the expression can be factored

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

After factoring, divide out like terms. \(\displaystyle x+4\)

\(\displaystyle \frac{(x-4)}{2}\)

Final Answer

Example Question #2 : Expressions

Simplify the following rational expression: (9x - 2)/(x2) MINUS (6x - 8)/(x2)

Possible Answers:

\(\displaystyle 3x-10\)

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

\(\displaystyle \frac{15x+6}{x}\)

\(\displaystyle \frac{12x-6}{x}\)

Correct answer:

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

Explanation:

Since both expressions have a common denominator, x2, we can just recopy the denominator and focus on the numerators. We get (9x - 2) - (6x - 8). We must distribute the negative sign over the 6x - 8 expression which gives us 9x - 2 - 6x + 8 ( -2 minus a -8 gives a +6 since a negative and negative make a positive). The numerator is therefore 3x + 6.

Example Question #1 : Expressions

Simplify the expression.

\(\displaystyle \frac{x}{2x+4}+\frac{x}{x+2}\)

Possible Answers:

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

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

\(\displaystyle \frac{x}{x+2}\)

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

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

Correct answer:

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

Explanation:

To add rational expressions, first find the least common denominator. Because the denominator of the first fraction factors to 2(x+2), it is clear that this is the common denominator. Therefore, multiply the numerator and denominator of the second fraction by 2.

\(\displaystyle \frac{x}{2x+4}+\frac{x}{x+2}\)

\(\displaystyle \frac{x}{2x+4}+\frac{(2)x}{(2)(x+2)}\)

\(\displaystyle \frac{x}{2x+4}+\frac{2x}{2x+4}\)

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

This is the most simplified version of the rational expression.

 

Example Question #11 : Expressions

If √(ab) = 8, and a= b, what is a?

Possible Answers:

10

4

64

2

16

Correct answer:

4

Explanation:

If we plug in a2 for b in the radical expression, we get √(a3) = 8. This can be rewritten as a3/2 = 8. Thus, loga 8 = 3/2. Plugging in the answer choices gives 4 as the correct answer. 

Example Question #3 : Expressions

Function_part1

 

Possible Answers:

9/5

37/15

–11/5

–37/15

–9/5

Correct answer:

–11/5

Explanation:

Fraction_part2

Fraction_part3

Example Question #3 : Rational Expressions

Simplify.

\(\displaystyle \frac{x+5}{x}-\frac{2x-3}{x^{2}}\)

Possible Answers:

\(\displaystyle 3x+3\)

\(\displaystyle \frac{x^{2}+7x+3}{x^{2}}\)

\(\displaystyle 7x+3\)

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

\(\displaystyle x+6\)

Correct answer:

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

Explanation:

\(\displaystyle \frac{x+5}{x}-\frac{2x-3}{x^{2}}\)

Determine an LCD (Least Common Denominator) between \(\displaystyle x\) and \(\displaystyle x^{2}\).

LCD = \(\displaystyle x^{2}\)

\(\displaystyle \frac{x(x+5)}{(x)x}-\frac{2x-3}{x^{2}}\)

Multiply the top and bottom of the first rational expression by \(\displaystyle x\), so that the denominator will be \(\displaystyle x^{2}\).

Distribute the \(\displaystyle x\) to \(\displaystyle x+5\).

\(\displaystyle \frac{x^{2}+5x}{x^{2}}-\frac{2x-3}{x^{2}}\)

Now you can subtract because both rational expressions have the same denominators.

\(\displaystyle \frac{x^{2}+5x-2x+3}{x^{2}}\)

Final Answer. 

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

Example Question #1 : How To Divide Rational Expressions

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

Possible Answers:

(xt)^{-1}\(\displaystyle (xt)^{-1}\)

x^{2}-t^{2}\(\displaystyle x^{2}-t^{2}\)

\frac{x}{t}\(\displaystyle \frac{x}{t}\)

t-x\(\displaystyle t-x\)

x-t\(\displaystyle x-t\)

Correct answer:

(xt)^{-1}\(\displaystyle (xt)^{-1}\)

Explanation:

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

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}\(\displaystyle \frac{1}{t}\) has a denominator of \dpi{100} t\(\displaystyle \dpi{100} t\), and \dpi{100} -\frac{1}{x}\(\displaystyle \dpi{100} -\frac{1}{x}\) has a denominator of \dpi{100} x\(\displaystyle \dpi{100} x\). The least common denominator that these two fractions have in common is \dpi{100} xt\(\displaystyle \dpi{100} xt\). Thus, we are going to write equivalent fractions with denominators of \dpi{100} xt\(\displaystyle \dpi{100} xt\).

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

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

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

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

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

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

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

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

To simplify this further, we can think of \frac{\frac{x-t}{xt}}{x-t}\(\displaystyle \frac{\frac{x-t}{xt}}{x-t}\) as the same as \frac{x-t}{xt}\div (x-t)\(\displaystyle \frac{x-t}{xt}\div (x-t)\) . 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}\(\displaystyle a\div b=a\cdot \frac{1}{b}\).

 

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

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

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

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

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