PSAT Math : Arithmetic

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #191 : Arithmetic

Mulitply and simplify. Assume all integers are positive real numbers. 

\(\displaystyle \sqrt{3}(3\sqrt{2}+\sqrt{3})\)

Possible Answers:

\(\displaystyle 27\sqrt{2}\)

\(\displaystyle 9\sqrt{2}+3\)

\(\displaystyle 9\sqrt{6}\)

\(\displaystyle 3\sqrt{6}+9\)

\(\displaystyle 3\sqrt{6}+3\)

Correct answer:

\(\displaystyle 3\sqrt{6}+3\)

Explanation:

\(\displaystyle \sqrt{3}(3\sqrt{2}+\sqrt{3})\)

Order of operations, first distributing the \(\displaystyle \sqrt{3}\) to all terms inside the parentheses. 

\(\displaystyle (1\cdot 3\sqrt{3}\cdot \sqrt{2})+(\sqrt{3}\cdot\sqrt{3})\)

\(\displaystyle 3\sqrt{3\cdot 2}+\sqrt{3\cdot 3}\rightarrow3\sqrt{6}+\sqrt{9}\rightarrow3\sqrt{6}+3\)

The final answer is \(\displaystyle 3\sqrt{6}+3\).

Example Question #3 : How To Multiply Square Roots

The square root(s) of 36 is/are ________.

Possible Answers:

6

6, -6, and 0

None of these answers are correct.

6 and -6

-6

Correct answer:

6 and -6

Explanation:

To square a number is to multiply that number by itself. Because 6 x 6 = 36 AND -6 x -6 = 36, both 6 and -6 are square roots of 36.

Example Question #11 : Square Roots And Operations

Simplify:

\(\displaystyle \sqrt{4}*\sqrt{12}*\sqrt{5}\)

Possible Answers:

\(\displaystyle \sqrt{21}\)

\(\displaystyle \sqrt{15}\)

\(\displaystyle 5\sqrt{12}\)

\(\displaystyle 4\sqrt{15}\)

\(\displaystyle 2\sqrt{60}\)

Correct answer:

\(\displaystyle 4\sqrt{15}\)

Explanation:

Multiplication of square roots is easy! You just have to multiply their contents by each other. Just don't forget to put the result "under" a square root! Therefore:

\(\displaystyle \sqrt{4}*\sqrt{12}*\sqrt{5}\)

becomes

\(\displaystyle \sqrt{4*12*5}=\sqrt{240}\)

Now, you need to simplify this:

\(\displaystyle \sqrt{240} = \sqrt{2*2*2*2*3*5}\)

You can "pull out" two \(\displaystyle 2\)s.  (Note, that it would be even easier to do this problem if you factor immediately instead of finding out that \(\displaystyle 4*12*5 = 240\).)

After pulling out the \(\displaystyle 2\)s, you get:

\(\displaystyle \sqrt{2*2*2*2*3*5} = 2*2(\sqrt{3*5}) = 4\sqrt{15}\)

Example Question #1 : Basic Squaring / Square Roots

Solve for \dpi{100} x\(\displaystyle \dpi{100} x\):

x\sqrt{45}+x\sqrt{72}=\sqrt{18}\(\displaystyle x\sqrt{45}+x\sqrt{72}=\sqrt{18}\)

Possible Answers:

x=3\(\displaystyle x=3\)

x=\sqrt{9}\(\displaystyle x=\sqrt{9}\)

x=\frac{\sqrt{5}}{\sqrt{2}}+2\(\displaystyle x=\frac{\sqrt{5}}{\sqrt{2}}+2\)

x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\(\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\)

x=\frac{\sqrt{2}}{\sqrt{5}}+\frac{1}{2}\(\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}}+\frac{1}{2}\)

Correct answer:

x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\(\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\)

Explanation:

x\sqrt{45}+x\sqrt{72}=\sqrt{18}\(\displaystyle x\sqrt{45}+x\sqrt{72}=\sqrt{18}\)

Notice how all of the quantities in square roots are divisible by 9

x\sqrt{9\times 5}+x\sqrt{9\times 8}=\sqrt{9\times 2}\(\displaystyle x\sqrt{9\times 5}+x\sqrt{9\times 8}=\sqrt{9\times 2}\)

x\sqrt{9}\sqrt{5}+x\sqrt{9}\sqrt{4\times 2}=\sqrt{9}\sqrt{2}\(\displaystyle x\sqrt{9}\sqrt{5}+x\sqrt{9}\sqrt{4\times 2}=\sqrt{9}\sqrt{2}\)

3x\sqrt{5}+3x\sqrt{4}\sqrt{2}=3\sqrt{2}\(\displaystyle 3x\sqrt{5}+3x\sqrt{4}\sqrt{2}=3\sqrt{2}\)

3x\sqrt{5}+6x\sqrt{2}=3\sqrt{2}\(\displaystyle 3x\sqrt{5}+6x\sqrt{2}=3\sqrt{2}\)

x(3\sqrt{5}+6\sqrt{2})=3\sqrt{2}\(\displaystyle x(3\sqrt{5}+6\sqrt{2})=3\sqrt{2}\)

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

Simplifying, this becomes

x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\(\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\)

Example Question #191 : Arithmetic

If m and n are postive integers and 4m = 2n, what is the value of m/n?

Possible Answers:

8

2

16

4

1/2

Correct answer:

1/2

Explanation:
  1. 2= 4. Also, following the rules of exponents, 4= 1. 
  2. One can therefore say that m = 1 and n = 2.
  3. The question asks to solve for m/n. Since m = 1 and n = 2, m/n = 1/2.

Example Question #1 : Factoring And Simplifying Square Roots

Simplify the radical:

\(\displaystyle \sqrt{320}\)

Possible Answers:

\(\displaystyle \sqrt{320}\)

\(\displaystyle 8\sqrt{5}\)

\(\displaystyle 4\sqrt{5}\)

\(\displaystyle 4\sqrt{20}\)

\(\displaystyle 8\sqrt{20}\)

Correct answer:

\(\displaystyle 8\sqrt{5}\)

Explanation:

\(\displaystyle \sqrt{320}=\sqrt{2\times 160}=\sqrt{2\times 2\times 80}=2\sqrt{80}=2\sqrt{2\times 40}=2\sqrt{2\times 2\times 20}=2\times 2\times \sqrt{20}=4\sqrt{2\times 10}=4\sqrt{2\times 2\times 5}=4\times 2\times \sqrt{5}=8\sqrt{5}\)

 

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

Simplify. 

\(\displaystyle \sqrt{\frac{16}{121}}\)

Possible Answers:

\(\displaystyle 16\sqrt{121}\)

\(\displaystyle \frac{4}{11}\)

\(\displaystyle \frac{4}{\sqrt{121}}\)

\(\displaystyle \frac{8}{61}\)

\(\displaystyle \frac{16}{121}\)

Correct answer:

\(\displaystyle \frac{4}{11}\)

Explanation:

\(\displaystyle \sqrt{\frac{16}{121}}\)

Take the square root of both the top and bottom terms.

\(\displaystyle \frac{\sqrt{16}}{\sqrt{121}}\)

Simplify. 

\(\displaystyle \frac{4}{11}\)

Example Question #2 : How To Find The Square Of An Integer

The square root of 5184 is:

Possible Answers:

71

74

70

72

73

Correct answer:

72

Explanation:

The easiest way to narrow down a square root from a list is to look at the last number on the squared number – in this case 4 – and compare it to the last number of the answer. 

70 * 70 will equal XXX0

71 * 71 will equal XXX1

72 * 72  will equal XXX4

73 * 73 will equal XXX9

74 * 74  will equal XXX(1)6

Therefore 72 is the answer.  Check by multiplying it out.

Example Question #81 : Basic Squaring / Square Roots

If 5^{x}+5^{x}+5^{x}+5^{x}+5^{x}=5^{10}\(\displaystyle 5^{x}+5^{x}+5^{x}+5^{x}+5^{x}=5^{10}\), what is the value of x?

Possible Answers:

5

2

1

10

9

Correct answer:

9

Explanation:

5(5^{x})=5^{10}\(\displaystyle 5(5^{x})=5^{10}\)

5^{1}(5^{x})=5^{10}\(\displaystyle 5^{1}(5^{x})=5^{10}\)

5^{x+1}=5^{10}\(\displaystyle 5^{x+1}=5^{10}\)

x=9\(\displaystyle x=9\)

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

If x and y are integers and xy + y2 is even, which of the following statements must be true?

I. 3y is odd

II. y/2 is an integer

III. xy is even

Possible Answers:

II only

I only

I, II, & III

\(\displaystyle None\ of\ the\ statements\ must\ be\ true\)

I & II 

Correct answer:

\(\displaystyle None\ of\ the\ statements\ must\ be\ true\)

Explanation:

In order for the original statement to be true, the \(\displaystyle xy\) and \(\displaystyle y^{2}\) terms must be either both odd or both even. Looking at each of the statements individually,

I. States that \(\displaystyle 3y\) is odd, but only odd values multiplied by 3 are odd. If \(\displaystyle y\) was an even number, the result would be even. But \(\displaystyle y\) can be either odd or even, depending on what \(\displaystyle x\) equals. Thus this statement COULD be true but does not HAVE to be true.

II. States that \(\displaystyle \frac{y}{2}\) is an integer, and since only even numbers are cleanly divided by 2 (odd values result in a fraction) this ensures that \(\displaystyle y\) is even. However, \(\displaystyle y\) can also be odd, so this is a statement that COULD be true but does not HAVE to be true.

III. For exponents, only the base value determines whether it is even or odd - it does not indicate the value of y at all. Only even numbers raised to any power are even, thus, this ensures that \(\displaystyle x\) is even. But \(\displaystyle x\) can be odd as well, so this statement COULD be true but does not HAVE to be true.

An example of two integers that will work violate conditions II and III is \(\displaystyle x=1\) and \(\displaystyle y=3\).

\(\displaystyle (1)\cdot (3)+(3)^{2}=3+9=12\), and even number.

\(\displaystyle \frac{3}{2}\) is not an integer.

\(\displaystyle 1^{3}=1\) is not even.

Furthermore, any combination of 2 even integers will make the original statement true, and violate the Statement I.

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