Algebra 1 : How to write expressions and equations

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #1041 : Linear Equations

Write the expression:  Sixteen less than a number squared.

Possible Answers:

\(\displaystyle x^2-16\)

\(\displaystyle 16-x^2\)

\(\displaystyle (x^2-16)^2\)

\(\displaystyle (x-16)^2\)

\(\displaystyle (16-x)^2\)

Correct answer:

\(\displaystyle x^2-16\)

Explanation:

Separate the sentence into parts.

A number squared:  \(\displaystyle x^2\)

Sixteen less than a number squared:  \(\displaystyle x^2-16\)

Note that the number 16 is subtract from \(\displaystyle x^2\) if 16 is less than the number.

The answer is:  \(\displaystyle x^2-16\)

Example Question #1042 : Linear Equations

Write as a variable expression:

Nine multiplied by the sum of a number and two thirds.

Possible Answers:

\(\displaystyle 9 \left ( x+\frac{2}{3}\right )\)

\(\displaystyle 9 x+\frac{2}{3}\)

\(\displaystyle 9 +\frac{2}{3} x\)

\(\displaystyle \frac{9 +2x}{3}\)

\(\displaystyle \frac{9 \left ( x+2 \right )}{3}\)

Correct answer:

\(\displaystyle 9 \left ( x+\frac{2}{3}\right )\)

Explanation:

"The sum of a number and two thirds" is the result of adding \(\displaystyle x\) and \(\displaystyle \frac{2}{3}\):

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

Nine multiplied by this, remembering to use parentheses to override the precedence of multiplication, is:

\(\displaystyle 9 \left ( x+\frac{2}{3}\right )\)

 

Example Question #1043 : Linear Equations

Write as a variable expression:

Twenty added to the product of seven tenths and a number

Possible Answers:

\(\displaystyle \frac{7x+20}{10}\)

\(\displaystyle \frac{7(x+20)}{10}\)

\(\displaystyle \frac{7}{10}(x+20)\)

\(\displaystyle \frac{7}{10}x+20\) 

\(\displaystyle \frac{7}{10}+20 x\)

Correct answer:

\(\displaystyle \frac{7}{10}x+20\) 

Explanation:

"The product of seven tenths and a number" is the result of multiplying \(\displaystyle \frac{7}{10}\) and \(\displaystyle x\):

\(\displaystyle \frac{7}{10}x\).

"Twenty added to" this is 

\(\displaystyle \frac{7}{10}x+20\)

Example Question #131 : How To Write Expressions And Equations

Which of the following English-language expressions can be rewritten as the algebraic expression \(\displaystyle \frac{2}{3} (x-7)\)  ?

Possible Answers:

Two thirds multiplied by the difference of a number and seven

The product of a number and seven, subtracted from two thirds

Two thirds subtracted from the product of a number and seven

Two thirds multiplied by the difference of seven and a number

None of the other responses is correct

Correct answer:

Two thirds multiplied by the difference of a number and seven

Explanation:

\(\displaystyle \frac{2}{3} (x-7)\) is two thirds multiplied by \(\displaystyle x-7\), which is the difference of a number and seven. Putting this together, this expression is stated as:

"Two thirds multiplied by the difference of a number and seven"

Example Question #1051 : Linear Equations

"If seven is multiplied by the sum of an unknown number and twelve, the result is four times that unknown number."

Rewrite the above statement as a variable equation.

Possible Answers:

\(\displaystyle 12(x+7) = 4x\)

\(\displaystyle 7x = 4x + 12\)

\(\displaystyle 12x = 4x + 7\)

\(\displaystyle 7(x+12) = 4x\)

\(\displaystyle 7x+12= 4x\)

Correct answer:

\(\displaystyle 7(x+12) = 4x\)

Explanation:

If we call this unknown number \(\displaystyle x\), then "the sum of an unknown number and twelve" is

\(\displaystyle x+12\)

"seven...multiplied by the sum of an unknown number and twelve" is seven multiplied by \(\displaystyle x+12\); remembering to override the order of operations with parentheses, the expression is 

\(\displaystyle 7(x+12)\)

The result is four times that unknown number, which is 

\(\displaystyle 4x\)

Putting it together, the equation is

\(\displaystyle 7(x+12) = 4x\)

 

Example Question #1052 : Linear Equations

Write the expression:  One more than the quantity of twice a number squared.

Possible Answers:

\(\displaystyle 2(x^2+1)\)

\(\displaystyle 2x(x+1)^2\)

\(\displaystyle 2(x+1)^2\)

\(\displaystyle (2x)^2+1\)

\(\displaystyle 2x^2+1\)

Correct answer:

\(\displaystyle (2x)^2+1\)

Explanation:

Split the sentence into parts.  Let a variable be the number.

Twice a number: \(\displaystyle 2x\)

The quantity of twice a number squared:  \(\displaystyle (2x)^2\)

One more than the quantity of twice a number squared: \(\displaystyle (2x)^2+1\)

The answer is:  \(\displaystyle (2x)^2+1\)

Example Question #1053 : Linear Equations

Write the expression:  Four less than half a number.

Possible Answers:

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

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

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

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

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

Correct answer:

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

Explanation:

Separate the sentence into parts.  Use a variable to denote the number.

Half a number:  \(\displaystyle \frac{1}{2}x\)

Four less than half a number:  \(\displaystyle \frac{1}{2}x-4\)

The answer is:  \(\displaystyle \frac{1}{2}x-4\)

Example Question #1054 : Linear Equations

Write the following equation:  Five more than twice a number is nine.

Possible Answers:

\(\displaystyle (2+5)x=9\)

\(\displaystyle 2(x+5)=9\)

\(\displaystyle 2x=5+9\)

\(\displaystyle x+10=9\)

\(\displaystyle 2x+5=9\)

Correct answer:

\(\displaystyle 2x+5=9\)

Explanation:

Separate the sentence into parts.

Twice a number:  \(\displaystyle 2x\)

Five more than twice a number:  \(\displaystyle 2x+5\)

Is nine:  \(\displaystyle =9\)

Combine the parts.

The answer is:  \(\displaystyle 2x+5=9\)

Example Question #1055 : Linear Equations

Write the expression:  Six more than the cube root of twice a number.

Possible Answers:

\(\displaystyle 2\sqrt[3]{x}+6\)

\(\displaystyle \sqrt[3]{2x+6}\)

\(\displaystyle 2\sqrt[3]{x+6}\)

\(\displaystyle \sqrt[3]{2x}+6\)

\(\displaystyle 2\sqrt[3]{2(x+6)}\)

Correct answer:

\(\displaystyle \sqrt[3]{2x}+6\)

Explanation:

Seperate the sentence into parts.

Twice a number:  \(\displaystyle 2x\)

The cube root of twice a number:  \(\displaystyle \sqrt[3]{2x}\)

Six more than the cube root of twice a number:  \(\displaystyle \sqrt[3]{2x}+6\)

The answer is:  \(\displaystyle \sqrt[3]{2x}+6\)

Example Question #1056 : Linear Equations

"If the product of one-tenths and a number is subtracted from six, the result is seven more than that number."

Rewrite the above statement as a variable equation.

Possible Answers:

\(\displaystyle \frac{1}{10}x -6 = x + 7\)

\(\displaystyle \frac{1}{10}(x -6) = x + 7\)

\(\displaystyle 6 - \frac{1}{10}x = x + 7\)

\(\displaystyle \frac{1}{10}(x -6) = 7x\)

\(\displaystyle \frac{1}{10}x -6 = 7x\)

Correct answer:

\(\displaystyle 6 - \frac{1}{10}x = x + 7\)

Explanation:

If we call this unknown number \(\displaystyle x\), then "the product of one-tenths and a number" is \(\displaystyle \frac{1}{10}x\).

"The product of one-tenths and a number...subtracted from six" is \(\displaystyle \frac{1}{10}x\) subtracted from six, or 

\(\displaystyle 6 - \frac{1}{10}x\).

This result is equal to seven more than that number, which is \(\displaystyle x+7\), so the equation is

\(\displaystyle 6 - \frac{1}{10}x = x + 7\).

 

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