GRE Math : How to square a decimal

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #371 : Arithmetic

Which quantity is greater? When \(\displaystyle 0< x< 1\)

Quantity A  

\(\displaystyle x^2\) 

Quantity B 

1

Possible Answers:

The relationship cannot be determined from the information given.

The two quantities are equal.

Quantity B is greater.

Quantity A is greater.

Correct answer:

Quantity B is greater.

Explanation:

X must equal a number between 0 and 1.  

If you square any decimal number in this range you will get an answer less than 1.  Try \(\displaystyle (0.999)^2\)= 0.998.

Therefore Quantity B is always larger.

Example Question #2 : Basic Squaring / Square Roots

Which is greater, when \(\displaystyle \small \small \small 0< x< 1?\)

Quantity A

\(\displaystyle \small x^2\)

Quantity B

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

Possible Answers:

Quantity A is greater

The two quantities are equal

Quantity B is greater

The relationship cannot be determined from the information given

Correct answer:

The relationship cannot be determined from the information given

Explanation:

When \(\displaystyle \small 0< x< 1\)\(\displaystyle \small x\) must be a decimal. Therefore it will decrease when it is squared. To find this answer we can substitute two values for \(\displaystyle \small x\).

\(\displaystyle \small x = 0.9\) and \(\displaystyle \small x = 0.1\)

When \(\displaystyle \small x = 0.9\)

\(\displaystyle \small \small 0.9^2 = 0.81 > \frac{0.9}{2} = 0.45\)

But when \(\displaystyle \small x = 0.1\)

\(\displaystyle \small 0.1^2 = 0.01 < \frac{0.1}{2} = 0.05\)

Therefore we cannot tell which is greater based on the information given.

 

Example Question #3 : Basic Squaring / Square Roots

Which is greater, when \(\displaystyle \small \small 0< x< 1?\)

Quantity A

\(\displaystyle \small \small x\)

Quantity B

\(\displaystyle \small 2x^2\)

Possible Answers:

Quantity B is greater

Quantity A is greater

The relationship cannot be determined from the information given

The two quantities are equal

Correct answer:

The relationship cannot be determined from the information given

Explanation:

When \(\displaystyle \small 0< x< 1\)\(\displaystyle \small x\) must be a decimal. Therefore it will decrease when it is squared. To find this answer we can substitute two values for \(\displaystyle \small x\).

\(\displaystyle \small x = 0.9\) and \(\displaystyle \small x = 0.1\)

When \(\displaystyle \small x = 0.9\)

\(\displaystyle \small \small \small 2\cdot0.9^2 = 1.62 > 0.9\)

But when \(\displaystyle \small x = 0.1\)

\(\displaystyle \small \small 2\cdot0.1^2 = 0.02 < 0.1\)

Therefore we cannot tell which is greater based on the information given.

 

Example Question #961 : Gre Quantitative Reasoning

Which is greater, when \(\displaystyle \small -1< x< 0?\)

Quantity A

\(\displaystyle \small \left | x\right |\)

Quantity B

\(\displaystyle \small x^2\)

Possible Answers:

The relationship cannot be determined from the information given

Quantity B is greater

Quantity A is greater

The two quantities are equal

Correct answer:

Quantity A is greater

Explanation:

When \(\displaystyle \small \small -1< x< 0\)\(\displaystyle \small x\) must be a negative decimal. Therefore it will decrease when it is squared and become positive. The first quantity \(\displaystyle \small \left | x\right |\) is the distance to 0 from \(\displaystyle \small x\), in other words the positive value of \(\displaystyle \small x\). The second quantity \(\displaystyle \small x^2\) will always be positive, but because it is a decimal it will always be less than \(\displaystyle \small x\), if \(\displaystyle \small x\) was a positive quantity. Since \(\displaystyle \small \left | x\right |\equiv x\), then \(\displaystyle \small \left | x\right |\) wiill always be greater than \(\displaystyle \small x^2\).

Quantity A is greater.

Example Question #4 : Basic Squaring / Square Roots

Which is greater, when \(\displaystyle \small \small -1< x< 0?\)

Quantity A

\(\displaystyle \small x^2\)

Quantity B

\(\displaystyle \small 1\)

Possible Answers:

The relationship cannot be determined from the information given

Quantity A is greater

The two quantities are equal

Quantity B is greater

Correct answer:

Quantity B is greater

Explanation:

When \(\displaystyle \small \small -1< x< 0\)\(\displaystyle \small x\) must be a negative decimal. Therefore it will decrease when it is squared and become positive. Because \(\displaystyle \small x\) must be a decimal, \(\displaystyle \small x^2\) will also be a decimal. Therefore \(\displaystyle \small x^2\) will never be greater than 1.

Quantity B is greater.

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