GRE Math : Operations

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #463 : Arithmetic

Simplify:

\(\displaystyle \frac{44}{18}*\frac{3}{11}*\frac{5}{8}\)

Possible Answers:

\(\displaystyle \frac{132}{65}\)

\(\displaystyle \frac{41}{20}\)

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

\(\displaystyle \frac{125}{22}\)

\(\displaystyle \frac{88}{15}\)

Correct answer:

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

Explanation:

Multiplying fractions is very easy. All you do is multiply all the numerators by each other and all the denominators by each other. You do not have to do anything that has to do with fancy common denominators like you do for adding and subtracting. For a question like this, it is often easiest just to cancel factors before you start your final multiplication. First, note:

\(\displaystyle \frac{44}{18}*\frac{3}{11}*\frac{5}{8}=\frac{44*3*5}{18*11*8}\)

Now, cancel the \(\displaystyle 11\) from the \(\displaystyle 44\):

\(\displaystyle \frac{4*3*5}{18*8}\)

Next, the \(\displaystyle 4\) in the numerator cancels with the \(\displaystyle 8\) in the denominator:

\(\displaystyle \frac{3*5}{18*2}\)

Finally, the \(\displaystyle 3\) in the numerator cancels with the \(\displaystyle 18\) in the denominator:

\(\displaystyle \frac{5}{6*2}=\frac{5}{12}\)

Example Question #464 : Arithmetic

Simplify:

\(\displaystyle \frac{15}{2}*\frac{12}{45}*\frac{3}{4}\)

Possible Answers:

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

\(\displaystyle \frac{3}{15}\)

\(\displaystyle \frac{3}{5}\)

\(\displaystyle \frac{5}{2}\)

\(\displaystyle \frac{100}{3}\)

Correct answer:

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

Explanation:

Multiplying fractions is very easy. All you do is multiply all the numerators by each other and all the denominators by each other. You do not have to do anything that has to do with fancy common denominators like you do for adding and subtracting. For a question like this, it is often easiest just to cancel factors before you start your final multiplication. First, note:

\(\displaystyle \frac{15}{2}*\frac{12}{45}*\frac{3}{4}=\frac{15*12*3}{2*45*4}\)

Now, cancel the \(\displaystyle 4\) in the denominator with the \(\displaystyle 12\) in the numerator:

\(\displaystyle \frac{15*3*3}{2*45}\)

Next, the \(\displaystyle 3*3\) in the numerator cancels with the \(\displaystyle 45\) in the denominator:

\(\displaystyle \frac{15}{2*5}\)

Finally, cancel the \(\displaystyle 5\) in the denominator with the \(\displaystyle 15\) in the numerator:

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

Example Question #1 : How To Multiply Fractions

Solve for \(\displaystyle x\):

\(\displaystyle \frac{1}{3}(4x+\frac{12}{5})=2\)

Possible Answers:

\(\displaystyle 7\)

\(\displaystyle \frac{9}{10}\)

\(\displaystyle 13\)

\(\displaystyle \frac{122}{9}\)

\(\displaystyle \frac{15}{2}\)

Correct answer:

\(\displaystyle \frac{9}{10}\)

Explanation:

Begin by distributing the group on the left side of the equation. Remember that it is easy to multiply fractions. You only need to multiply the denominators and numerators. There are no "fancy" steps in between.

Therefore,

\(\displaystyle \frac{1}{3}(4x+\frac{12}{5})=2\)

is the same as:

\(\displaystyle (\frac{1}{3}*4x+\frac{1}{3}*\frac{12}{5})=2\)

You can cancel part of the second fraction out, so you get:

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

Now, subtract \(\displaystyle \frac{4}{5}\) from both sides:

\(\displaystyle \frac{4x}{3}=2-\frac{4}{5}\)

Simplifying the right side of the equation, you get...

\(\displaystyle \frac{4x}{3}=\frac{10}{5}-\frac{4}{5}\)

\(\displaystyle \frac{4x}{3}=\frac{6}{5}\)

Now, multiply both sides by \(\displaystyle \frac{3}{4}\):

\(\displaystyle \frac{3}{4}*\frac{4x}{3}=\frac{6}{5}*\frac{3}{4}\)

Simplify:

\(\displaystyle x=\frac{18}{20} = \frac{9}{10}\)

Example Question #1 : How To Divide Fractions

Car A traveled 120 miles with 5 gallons of fuel.

Car B can travel 25 miles per gallon of fuel.

Quantity A: The fuel efficiency of car A

Quantity B: The fuel efficiency of car B

Possible Answers:

Quantity A is greater.

The two quantities are equal.

Quantity B is greater.

The relationship cannot be determined.

Correct answer:

Quantity B is greater.

Explanation:

Let's make the two quantities look the same. 

Quantity A: 120 miles / 5 gallons =  24 miles / gallon

Quantity B: 25 miles / gallon

Quantity B is greater.

Example Question #11 : Operations

Quantity A:

The \(\displaystyle x\)-value of the equation \(\displaystyle y = \frac{3}{4}x-2\) when \(\displaystyle y = \frac{-1}{3}\)

Quantity B:

 \(\displaystyle \frac{3}{4}\)

Possible Answers:

Quantity B is greater.

Quantity A is greater.

Both quantities are equal

The relationship cannot be determined from the information given.

Correct answer:

Quantity A is greater.

Explanation:

In order to solve quantitative comparison problems, you must first deduce whether or not the problem is actually solvable. Since this consists of finding the solution to an \(\displaystyle x\)-coordinate on a line where nothing too complicated occurs, it will be possible.  

Thus, your next step is to solve the problem.

Since \(\displaystyle y = \frac{3}{4}x-2\) and \(\displaystyle y = \frac{-1}{3}\), you can plug in the \(\displaystyle y\)-value and solve for \(\displaystyle x\):

\(\displaystyle y = \frac{3}{4}x-2\)

Plug in y:

\(\displaystyle \frac{-1}{3} = \frac{3}{4}x-2\)

Add 2 to both sides:

\(\displaystyle \frac{5}{3} = \frac{3}{4}x\)

Divide by 3/4.  To divide, first take the reciprocal of 3/4 (aka, flip it) to get 4/3, then multiply that by 5/3:

\(\displaystyle \frac{20}{9} = x\)

Make the improper fraction a mixed number:

\(\displaystyle 2\tfrac{2}{9}\)

 Now that you have what x equals, you can compare it to Quantity B. 

Since \(\displaystyle 2\tfrac{2}{9}\) is bigger than 2, the answer is that Quantity A is greater

 

Example Question #12 : Operations

What is equivalent to \(\displaystyle \frac{\frac{1}{5}}{\frac{4}{15}}\)?

Possible Answers:

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

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

\(\displaystyle \frac{6}{5}\)

\(\displaystyle \frac{3}{4}\)

\(\displaystyle \frac{4}{75}\)

Correct answer:

\(\displaystyle \frac{3}{4}\)

Explanation:

Remember that when you divide by a fraction, you multiply by the reciprocal of that fraction.  Therefore, this division really is:

\(\displaystyle \frac{1}{5}\cdot \frac{15}{4}\)

At this point, it is merely a matter of simplification and finishing the multiplication:

\(\displaystyle \frac{1}{5}\cdot\frac{15}{4}=\frac{15}{20}=\frac{3}{4}\)

Example Question #1052 : Gre Quantitative Reasoning

Which of the following is equivalent to \(\displaystyle \frac{7}{\frac{4}{5}}\)?

Possible Answers:

\(\displaystyle \frac{4}{35}\)

\(\displaystyle \frac{28}{5}\)

\(\displaystyle \frac{35}{4}\)

\(\displaystyle \frac{5}{28}\)

\(\displaystyle \frac{11}{5}\)

Correct answer:

\(\displaystyle \frac{35}{4}\)

Explanation:

To begin with, most students find it easy to remember that...

\(\displaystyle \frac{7}{\frac{4}{5}}=\frac{\frac{7}{1}}{\frac{4}{5}}\)

From this, you can apply the rule of division of fractions.  That is, multiply by the reciprocal:

Therefore,

\(\displaystyle \frac{\frac{7}{1}}{\frac{4}{5}} = \frac{7}{1} \cdot \frac{5}{4}=\frac{35}{4}\)

Since nothing needs to be reduced, this is your answer.

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