GRE Math : Even / Odd Numbers

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #3 : How To Divide Odd Numbers

Solve for :

Possible Answers:

Correct answer:

Explanation:

To solve, divide both sides of the equation by :

As a check, if you divide an odd number by another odd number, your result should be odd. 

Example Question #1 : How To Divide Odd Numbers

Solve for :

Possible Answers:

Correct answer:

Explanation:

To solve, isolate your variable by dividing both sides of the equation by :

Example Question #5 : How To Divide Odd Numbers

Solve for :

Possible Answers:

Correct answer:

Explanation:

To solve, first isolate your variable by dividing both sides of the equation by :

As a check, if you divide an odd number by another odd number, your result should be odd. 

Example Question #6 : How To Divide Odd Numbers

Solve for :

Possible Answers:

Correct answer:

Explanation:

To solve, divide both sides of the equation by :

As a check, if you divide an odd number by another odd number, your result should be odd. 

Example Question #5 : Even / Odd Numbers

If  and  are both odd integers, which of the following is not necessarily odd?

Possible Answers:

Correct answer:

Explanation:

With many questions like this, it might be easier to plug in numbers rather than dealing with theoretical variables.  However, given that this question asks for the expression that is not always even or odd but only not necessarily odd, the theoretical route might be our only choice.

Therefore, our best approach is to simply analyze each answer choice.

:  Since  is odd,  is also odd, since and odd number multiplied by an odd number yields an odd product.  Since  is also odd, multiplying it by  will again yield an odd product, so this expression is always odd.

:  Since  is odd, multiplying it by 2 will yield an even number.  Subtracting this number from  will also give an odd result, since an odd number minus an even number gives an odd number.  Therefore, this answer is also always odd.

:  Since both numbers are odd, their product will also always be odd.

:  Since  is odd, multiplying it by 2 will give an even number.  Since  is odd, subtracting it from our even number will give an odd number, since an even number minus and odd number is always odd.  Therefore, this answer will always be odd.

:   Since both numbers are odd, there sum will be even.  However, dividing an even number by another even number (2 in our case) does not always produce an even or an odd number.  For example, 5 and 7 are both odd.  Their sum, 12, is even.  Dividing by 2 gives 6, an even number.  However, 5 and 9 are also both odd.  Their sum, 14, is even, but dividing by 2 gives 7, an odd number.  Therefore, this expression isn't necessarily always odd or always even, and is therefore our answer.

Example Question #1 : Integers

Theodore has  jelly beans. Portia has three times that amount. Harvey has five times as many as she does. What is the total count of jelly beans in the whole group?

Possible Answers:

Correct answer:

Explanation:

To find the answer to this question, calculate the total jelly beans for each person:

Portia:  * <Theodore's count of jelly beans>, which is  or 

Harvey:  * <Portia's count of jelly beans>, which is  or 

So, the total is:

(Do not forget that you need those original  for Theodore!)

Example Question #1 : How To Multiply Odd Numbers

Assume  and  are both odd whole numbers.

What is a possible solution for ?

Possible Answers:

Correct answer:

Explanation:

When  two odd whole numbers are multipliedd, they will equal an odd whole number. The only answer that fits the requirements of being an odd and a whole number is  since it comes from  or .

Example Question #22 : Even / Odd Numbers

If  is even, and  is odd. Which of the following must be odd?

Possible Answers:

Correct answer:

Explanation:

To solve, pick numbers to represent  and . Let  and . Now try each of the equations given:

Only  works and is thus our answer.

Example Question #1 : How To Multiply Even Numbers

 is even

 is even

Quantity A:

The remainder of 

Quantity B:

1

Possible Answers:

The relationship between the quantities cannot be determined.

Quantity B is larger.

Quantity A is larger.

The two quantities are equal.

Correct answer:

Quantity B is larger.

Explanation:

Begin by considering our options.  For , it is either the case that:

 is even and  is odd, or,

 is even and  is even, or,

 is odd and  is even

Now, for , it is either the case that:

 and  are even, or,

 and  are odd

Now, for , it cannot be the case that both are odd.  This means that the only viable option for  is the case when both are even.  

Therefore,  must be even, meaning that the remainder of  must be .  

Therefore, quantity B is larger.

Example Question #1 : How To Multiply Even Numbers

 is even

 is even

Therefore, which of the following must be true about ?

Possible Answers:

It could be either even or odd.

It must be even.

It must be odd.

Correct answer:

It could be either even or odd.

Explanation:

Recall that when you multiply by an even number, you get an even product.

Therefore, we know the following from the first statement:

 is even or  is even or both  and  are even.

 

For the second, we know this:

Since  is even, therefore,  can be either even or odd. (Regardless of what it is, we can get an even value for .)  

Based on all this data, we can tell nothing necessarily about . If  is even, then  is even, even if  is odd. However, if  is odd while  is even, then  will be even.

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