GRE Math : Arithmetic

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #61 : Arithmetic

Which of the following is equivalent to the ratio of  to ?

Possible Answers:

Correct answer:

Explanation:

At first, this problem seems rather easy. You merely need to divide these two values to get:

However, there are no answers that look like this! When this happens, you should consider rationalizing the denominator to eliminate the square root. This is a little more difficult than normal problems like this (ones that contain only the radical). However, if you complete a difference of squares in the denominator, you will be well on your way to having the right answer:

Carefully FOIL your denominator and distribute your numerator:

Look to your answers for an idea for factoring your numerator:

Example Question #62 : Arithmetic

What is  if  ?

Possible Answers:

Correct answer:

Explanation:

Note that 

This changes the initial equation to

For this equation to be valid, the exponents must be equal:

Example Question #63 : Arithmetic

Given the equation , solve for .

Possible Answers:

Correct answer:

Explanation:

In order to solve for , the equation  must be written such that each set of exponents shares the same base:

Which like bases, it's now just a matter of solving for :

 

Example Question #61 : Basic Squaring / Square Roots

Which of the following is equal to ?

Possible Answers:

Correct answer:

Explanation:

To find an equivalent, just multiply the top and bottom by the conjugate of the denominator.

Conjugate is the square root expression found in the denominator but with opposite sign.

So:

By simplifying, we get .

Example Question #1 : How To Find A Ratio Of Square Roots

Which of the following has the same ratio as ?

Possible Answers:

Correct answer:

Explanation:

Since in all the answer choices have an integer in the denominator, we should multiply top and bottom by the conjugate of the denominator which is the square root expression with opposite sign.

So:

If we redistribute the negative, then the answer becomes 

.

Example Question #66 : Arithmetic

What is the ratio of  expressed in  form?

Possible Answers:

Correct answer:

Explanation:

To get into  form, multiply the fraction by bottom denominator's reciprocal.

The  is the numerator of the fraction and  is the denominator.

Final answer is 

Example Question #1 : Factors / Multiples

If a is the greatest common divisor of 64 and 14 and b is the least common multiple of 16 and 52 then a + b = ?

Possible Answers:

210

120

233

187

Correct answer:

210

Explanation:

The greatest common divisor of 64 and 14 is 2, as found by the prime factorization of 64 and 14. The least common multiple of 16 and 52 is 208, which can be found by looking at the decimal when 52 is divided by 16. The remainder is 0.25, or 1/4 so the fourth multiple of 52 is 208, which is also divisible by 16.

Example Question #1 : Integers

What is the least common multiple of 3, 4x, 5y, 6xy, and 10y?

Possible Answers:

60xy

30xy

60x2y2

30x2y2

25xy

Correct answer:

60xy

Explanation:

Each of the numbers on the list must be able to "fit" (multiply evenly) into a larger number at the same time. I.e. the largest number (multiple) divided by any of the listed numbers will result in a whole number. For the coefficients, the maximum value is 10, and multiplying the highest two coefficients give us 60. Since 60 is divisible evenly by the lower values, we know that it is the least common multiple for the list. For the variables, both x and y will fit evenly into a theoretical number, "xy". We do not need an exponential version of this multiple as there are no exponents in the original list.

Example Question #61 : Arithmetic

What is the least common multiple of 45 and 60?

Possible Answers:

25

15

360

225

180

Correct answer:

180

Explanation:

The least common multiple is the smallest number that is a multiple of all the numbers in the group.  Let's list some multiples of the two numbers and find the smallest number in common to both.

multiples of 45: 45, 90, 135, 180, 225, 270, ...

multiples of 60: 60, 120, 180, 240, 300, 360, ...

The smallest number in common is 180.

Example Question #1 : Integers

What is the least common multiple of  and ?

Possible Answers:

None of the other answers

Correct answer:

Explanation:

Factor each of our values into prime factors:

350 = 2 * 52 * 7

6270= 2 * 3 * 5 * 11 * 19

 

To find the least common multiple, we must choose the larger exponent for each of the prime factors involved.  Therefore, we will select 2, 52, and 7 from 350 and 3, 11, and 19 from 6270.

Therefore, our least common multiple is 2 * 3 * 52 * 7 * 11 * 19 = 219,450.

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