Common Core: 8th Grade Math : Expressions & Equations

Study concepts, example questions & explanations for Common Core: 8th Grade Math

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Example Questions

Example Question #51 : Grade 8

Solve: 

\displaystyle 4^{-8}\times4^{6}

Possible Answers:

\displaystyle -16

\displaystyle \frac{1}{16}

\displaystyle -\frac{1}{16}

\displaystyle 16

Correct answer:

\displaystyle \frac{1}{16}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 4^{-8}\times 4^{6}=4^{(-8+6)}

Solve for the exponents

\displaystyle -8+6=-2

\displaystyle 4^{-2}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{4^{2}}=\frac{1}{16}

Example Question #52 : Grade 8

Solve: 

\displaystyle 2^{-8}\times2^{3}

 

Possible Answers:

\displaystyle \frac{1}{32}

\displaystyle -32

\displaystyle 32

\displaystyle -\frac{1}{32}

Correct answer:

\displaystyle \frac{1}{32}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 2^{-8}\times 2^{3}=2^{(-8+3)}

Solve for the exponents

\displaystyle -8+3=-5

\displaystyle 2^{-5}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{2^{5}}=\frac{1}{32}

Example Question #21 : Generate Equivalent Numerical Expressions: Ccss.Math.Content.8.Ee.A.1

Solve: 

\displaystyle 3^{-6}\times3^{2}

 

Possible Answers:

\displaystyle \frac{1}{81}

\displaystyle -\frac{1}{81}

\displaystyle -81

\displaystyle 81

Correct answer:

\displaystyle \frac{1}{81}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 3^{-6}\times 3^{2}=3^{(-6+2)}

Solve for the exponents

\displaystyle -6+2=-4

\displaystyle 3^{-4}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{3^{4}}=\frac{1}{81}

Example Question #54 : Grade 8

Solve: 

\displaystyle 3^{-21}\times3^{16}

 

Possible Answers:

\displaystyle 243

\displaystyle \frac{1}{243}

\displaystyle -\frac{1}{243}

\displaystyle -243

Correct answer:

\displaystyle \frac{1}{243}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 3^{-21}\times 3^{16}=3^{(-21+16)}

Solve for the exponents

\displaystyle -21+16=-5

\displaystyle 3^{-5}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{3^{5}}=\frac{1}{243}

Example Question #22 : Generate Equivalent Numerical Expressions: Ccss.Math.Content.8.Ee.A.1

Solve: 

\displaystyle 5^{-19}\times5^{17}

 

Possible Answers:

\displaystyle \frac{1}{25}

\displaystyle -\frac{1}{27}

\displaystyle 27

\displaystyle -25

Correct answer:

\displaystyle \frac{1}{25}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 5^{-19}\times 5^{17}=5^{(-19+17)}

Solve for the exponents

\displaystyle -19+17=-2

\displaystyle 5^{-2}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{5^{2}}=\frac{1}{25}

Example Question #23 : Generate Equivalent Numerical Expressions: Ccss.Math.Content.8.Ee.A.1

Solve: 

\displaystyle 9^{-12}\times9^{9}

 

Possible Answers:

\displaystyle \frac{1}{716}

\displaystyle \frac{1}{346}

\displaystyle \frac{1}{81}

\displaystyle \frac{1}{729}

Correct answer:

\displaystyle \frac{1}{729}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 9^{-12}\times 9^{9}=9^{(-12+9)}

Solve for the exponents

\displaystyle -12+9=-3

\displaystyle 9^{-3}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{9^{3}}=\frac{1}{729}

Example Question #23 : Expressions & Equations

Which of the following expressions is equivalent to \displaystyle 2^{-13}\times2^{10}?

Possible Answers:

\displaystyle -8

\displaystyle -\frac{1}{8}

\displaystyle \frac{1}{8}

\displaystyle 8

Correct answer:

\displaystyle \frac{1}{8}

Explanation:

In order to solve this problem, we need to recall our exponent rules:

When our base numbers are equal to each other, like in this problem, we can add our exponents together using the following formula:

\displaystyle a^m\times a^n=a^{(m+n)}

Let's apply this rule to our problem

\displaystyle 2^{-13}\times 2^{10}=2^{(-13+10)}

Solve for the exponents

\displaystyle -13+10=-3

\displaystyle 2^{-3}

We cannot leave this problem in this format because we cannot have a negative exponent. Instead, we can move the base and the exponent to the denominator of a fraction:

\displaystyle a^{(-m)}=\frac{1}{a^m}

Solve the problem

\displaystyle \frac{1}{2^{3}}=\frac{1}{8}

Example Question #64 : Grade 8

Select the number that is equal to four times ten to the fifth power. 

 

Possible Answers:

\displaystyle 400

\displaystyle 40

Correct answer:

Explanation:

Four times ten to the fifth power can be written numerically as the following:

\displaystyle 4\times10^5

When a number between one and ten is multiplied by a power of ten it is said to be written in scientific notation. This number is currently written in scientific notation.

Even though this appears to be a challenging math problem (i.e. because we have a power of ten), we can simply move our decimal place after the four, or \displaystyle 4.0, over \displaystyle 5 spaces to the right using zeros as place holders. 

\displaystyle 4.0\times 10^5=400000.0

Add commas and simplify.

Example Question #65 : Grade 8

Select the number that is equal to three times ten to the seventh power. 

Possible Answers:

Correct answer:

Explanation:

Three times ten to the seventh power can be written numerically as the following:

\displaystyle 3\times10^7

When a number between one and ten is multiplied by a power of ten it is said to be written in scientific notation. This number is currently written in scientific notation.

Even though this appears to be a challenging math problem (i.e. because we have a power of ten), we can simply move our decimal place after the three, or \displaystyle 3.0, over \displaystyle 7 spaces to the right using zeros as place holders. 

\displaystyle 3.0\times 10^7=30000000.0

Add commas and simplify.

Example Question #66 : Grade 8

Select the number that is equal to two times ten to the eighth power. 

 

Possible Answers:

Correct answer:

Explanation:

Two times ten to the eighth power can be written numerically as the following:

\displaystyle 2\times10^8

When a number between one and ten is multiplied by a power of ten it is said to be written in scientific notation. This number is currently written in scientific notation.

Even though this appears to be a challenging math problem (i.e. because we have a power of ten), we can simply move our decimal place after the two, or \displaystyle 2.0, over \displaystyle 8 spaces to the right using zeros as place holders. 

\displaystyle 2.0\times 10^8=200000000.0

Add commas and simplify.

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