PSAT Math : Arithmetic

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Find The Square Of An Integer

How many integers from 20 to 80, inclusive, are NOT the square of another integer?

Possible Answers:

\(\displaystyle 59\)

\(\displaystyle 58\)

\(\displaystyle 56\)

\(\displaystyle 60\)

\(\displaystyle 57\)

Correct answer:

\(\displaystyle 57\)

Explanation:

First list all the integers between 20 and 80 that are squares of another integer:

52 = 25

62 = 36

72 = 49

82 = 64

In total, there are 61 integers from 20 to 80, inclusive. 61 – 4 = 57

Example Question #5 : How To Find The Square Of An Integer

Let the universal set \(\displaystyle U\) be the set of all positive integers.

Let \(\displaystyle A\) be the set of all multiples of 3; let \(\displaystyle B\) be the set of all multiples of 7; let \(\displaystyle C\) be the set of all perfect square integers. Which of the following statements is true of 243?

Note: \(\displaystyle A'\) means "the complement of \(\displaystyle A\)", etc.

Possible Answers:

\(\displaystyle 243 \in A' \cap B \cap C\)

\(\displaystyle 243 \in A \cap B \cap C\)

\(\displaystyle 243 \in A \cap B' \cap C'\)

\(\displaystyle 243 \in A \cap B' \cap C\)

\(\displaystyle 243 \in A' \cap B \cap C'\)

Correct answer:

\(\displaystyle 243 \in A \cap B' \cap C'\)

Explanation:

\(\displaystyle 243 \div 3 = 81\), so 243 is divisible by 3. \(\displaystyle 243 \in A\).

\(\displaystyle 243 \div 7= 34 \textup{ R }5\), so 243 is not divisible by 7. \(\displaystyle 243 \notin B\) - that is, \(\displaystyle 243 \in B'\).

\(\displaystyle 15 = \sqrt{225}< \sqrt{243} < \sqrt{256} = 16\), 243 is not a perfect square integer. \(\displaystyle 243 \notin C\) - that is, \(\displaystyle 243 \in C'\).

Since 243 is an element of \(\displaystyle A\)\(\displaystyle B'\), and \(\displaystyle C'\), it is an element of their intersection. The correct choice is that

\(\displaystyle 243 \in A \cap B' \cap C'\)

Example Question #162 : Arithmetic

Consider the inequality:

\(\displaystyle x< x^{5}< x^{4}\)

Which of the following could be a value of \(\displaystyle x\)?

Possible Answers:

x=-1\(\displaystyle x=-1\)

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

There is no possible value for x\(\displaystyle x\)

x=1\(\displaystyle x=1\)

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

Correct answer:

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

Explanation:

Notice how x^4\(\displaystyle x^4\) is the greatest value. This often means that x\(\displaystyle x\) is negative as (-1)^n=-1\(\displaystyle (-1)^n=-1\) when \dpi{100} n\(\displaystyle \dpi{100} n\) is odd and (-1)^n=1\(\displaystyle (-1)^n=1\) when \dpi{100} n\(\displaystyle \dpi{100} n\) is even.

Let us examine the first choice, x=-\frac{3}{4}\(\displaystyle x=-\frac{3}{4}\)

x^5=-\frac{3^5}{4^5}=-\frac{243}{1024}> -\frac{3}{4}\(\displaystyle x^5=-\frac{3^5}{4^5}=-\frac{243}{1024}> -\frac{3}{4}\)

This can only be true of a negative value that lies between zero and one.

Example Question #1 : How To Find The Square Of An Integer

\(\displaystyle \sqrt{y^2-63}=9\)

In the equation above, if \(\displaystyle y\) is a positive integer, what is the value of \(\displaystyle y\)?

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 11\)

\(\displaystyle -12\)

\(\displaystyle 12\)

\(\displaystyle 9\)

Correct answer:

\(\displaystyle 12\)

Explanation:

Begin by squaring both sides of the equation:

\(\displaystyle \sqrt{y^2-63}=9\)

\(\displaystyle (\sqrt{y^2-63})^2=9^2\)

\(\displaystyle y^2-63=81\)

Now solve for y:

\(\displaystyle y^2-63+63=81+63\)

\(\displaystyle y^2=144\)

\(\displaystyle y=12\)

Note that \(\displaystyle y\) must be positive as defined in the original question. In this case, \(\displaystyle y\) must be 12.

 

 

Example Question #2 : Factoring And Simplifying Square Roots

Simplify. Assume all variables are positive real numbers. 

\(\displaystyle \sqrt{16x^{5}{y^{2}}}\)

Possible Answers:

\(\displaystyle 4x^{2}y\sqrt{x}\)

\(\displaystyle 4x^{2}y\)

\(\displaystyle 4x^{5}y\)

\(\displaystyle 4x^{2}y^{2}\)

\(\displaystyle 4x^{5}y^{2}\)

Correct answer:

\(\displaystyle 4x^{2}y\sqrt{x}\)

Explanation:

\(\displaystyle \sqrt{16x^{5}{y^{2}}}\)

The index coefficent in \(\displaystyle \sqrt[n]{b}\) is represented by \(\displaystyle n\). When no index is present, assume it is equal to 2. \(\displaystyle b\) under the radical is known as the radican, the number you are taking a root of. 

First look for a perfect square, \(\displaystyle \sqrt{16}=4\)

Then to your Variables \(\displaystyle \sqrt{x^{5}y^{2}}\)

Take your exponents on both variables and determine the number of times our index will evenly go into both. 

\(\displaystyle \sqrt{x^{5}} \rightarrow 2\cdot2=4 +1\)

So you would take out a \(\displaystyle x^{2}\) and would be left with a \(\displaystyle \sqrt{x}\)

\(\displaystyle \sqrt{y^{2}} \rightarrow 2\cdot1=2\)

*Dividing the radican exponent by the index - gives you the number of variables that should be pulled out.

The final answer would be \(\displaystyle 4x^{2}y\sqrt{x}\).

Example Question #3 : Factoring And Simplifying Square Roots

Simplify. Assume all integers are positive real numbers. 

\(\displaystyle \sqrt[3]{24x^{16}y^{12}}\)

Possible Answers:

\(\displaystyle 2x^{5}y^{4}\)

\(\displaystyle 2x^{5}y^{4}\sqrt[3]{3x}\)

\(\displaystyle 8x^{16}y^{12}\)

\(\displaystyle 2x^{2}y^{3}\sqrt[3]{3xy}\)

\(\displaystyle 2x^{8}y^{4}\sqrt[3]{3x^{2}}\)

Correct answer:

\(\displaystyle 2x^{5}y^{4}\sqrt[3]{3x}\)

Explanation:

\(\displaystyle \sqrt[3]{24x^{16}y^{12}}\)

Index of \(\displaystyle 3\) means the cube root of Radican \(\displaystyle 24x^{16}y^{12}\)

Find a perfect cube in \(\displaystyle 24\) \(\displaystyle \rightarrow\) \(\displaystyle \sqrt[3]{8\cdot 3}\) 

Simplify the perfect cube, giving you \(\displaystyle 2\sqrt[3]{3}\).

Take your exponents on both variables and determine the number of times our index will evenly go into both.

 \(\displaystyle x\rightarrow \frac{16}{3}= 5^{\frac{1}{3}} \rightarrow x^{5}\sqrt[3]{x}\)

\(\displaystyle y\rightarrow \frac{12}{3}= 4 \rightarrow y^{4}\)


The final answer would be

\(\displaystyle 2x^{5}y^{4}\sqrt[3]{3x}\)

Example Question #1763 : Psat Mathematics

Simplify square roots. Assume all integers are positive real numbers. 

Simplify as much as possible. List all possible answers.

1a.\(\displaystyle \sqrt{12}\)

1b. \(\displaystyle \sqrt{48}\)

1c. \(\displaystyle \sqrt[3]{24}\)

Possible Answers:

\(\displaystyle 4\sqrt{3}\) and \(\displaystyle \sqrt{3}\) and\(\displaystyle 2\sqrt[3]{3}\)

\(\displaystyle 2\sqrt{3}\) and \(\displaystyle 4\sqrt{3}\) and \(\displaystyle 2\sqrt[3]{3}\)

\(\displaystyle 2\sqrt{3}\) and \(\displaystyle 4\sqrt{3}\) and \(\displaystyle 8\sqrt{3}\)

\(\displaystyle 2\sqrt{3}\) and \(\displaystyle 4\sqrt{3}\)

Correct answer:

\(\displaystyle 2\sqrt{3}\) and \(\displaystyle 4\sqrt{3}\) and \(\displaystyle 2\sqrt[3]{3}\)

Explanation:

When simplifying radicans (integers under the radical symbol), we first want to look for a perfect square. For example, \(\displaystyle \sqrt{12}\) is not a perfect square. You look to find factors of \(\displaystyle 12\) to see if there is a perfect square factor in \(\displaystyle 12\), which there is.

1a. \(\displaystyle \sqrt{12}=\sqrt{4\cdot 3}=\sqrt{4}\cdot\sqrt{3}= 2\sqrt{3}\)

Do the same thing for \(\displaystyle \sqrt{48}\).

1b.\(\displaystyle \sqrt{48}=\sqrt{16\cdot 3}=\sqrt{16}\cdot\sqrt{3}=4\sqrt{3}\)

1c.Follow the same procedure except now you are looking for perfect cubes. 

\(\displaystyle \sqrt[3]{24}=\sqrt[3]{8\cdot 3}=\sqrt[3]{8}\cdot\sqrt[3]{3}=2\sqrt[3]{3}\)

Example Question #1 : Simplifying Square Roots

Simplify

÷ √3

Possible Answers:

none of these

not possible

3√3

3

2

Correct answer:

3√3

Explanation:

in order to simplify a square root on the bottom, multiply top and bottom by the root

Asatsimplifysquare_root

Example Question #31 : Basic Squaring / Square Roots

Simplify:

√112

Possible Answers:

4√10

12

20

4√7

10√12

Correct answer:

4√7

Explanation:

√112 = {√2 * √56} = {√2 * √2 * √28} = {2√28} = {2√4 * √7} = 4√7 

Example Question #1 : Factoring And Simplifying Square Roots

Simplify:

 

√192

Possible Answers:
8√3
4√3
None of these
4√2
8√2
Correct answer: 8√3
Explanation:

√192 = √2 X √96 

√96 = √2 X √48

√48 = √4 X√12

√12 = √4 X √3

√192 = √(2X2X4X4) X √3

        = √4X√4X√4  X √3

        = 8√3

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