GRE Subject Test: Math : Combinations

Study concepts, example questions & explanations for GRE Subject Test: Math

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Example Questions

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Example Question #31 : Combinational Analysis

Find .

Possible Answers:

Correct answer:

Explanation:

There are two types of statistical calculations that are used when dealing with ordering a number of objects. When the order does not matter it is known as a combination and denoted by a C.

Thus the formula for this particular combination is,

The  will cancel out because it is in the numerator and denominator,

.

Example Question #32 : Combinational Analysis

Find .

Possible Answers:

Correct answer:

Explanation:

There are two types of statistical calculations that are used when dealing with ordering a number of objects. When the order does not matter it is known as a combination and denoted by a C.

Thus the formula for this particular combination is,

 

Example Question #11 : Combinations

Six points are located on a circle. How many line segments can be drawn?

Possible Answers:

Correct answer:

Explanation:

There are two types of statistical calculations that are used when dealing with ordering a number of objects. When the order does not matter it is known as a combination and denoted by a C.

Thus the formula for this particular combination is,

 

There are 2 points on each line segment.

 

Example Question #581 : Gre Subject Test: Math

Evaluate .

Possible Answers:

Correct answer:

Explanation:

Evaluate  is asking to calculate the combination of five objects when choosing three of them.

 

 or  cancels out.

 

Example Question #31 : Combinational Analysis

How many ways can I get non-repetitive three-digit numbers from the numbers: ?

Possible Answers:

Correct answer:

Explanation:

Step 1: Count how many numbers I can use..

I can use 9 numbers.

Step 2: Determine how many numbers I can put in the first digit of the three-digit number..

I can put  numbers in the first spot. I cannot put  in the first slot because the number will not be a three-digit number.

Step 3: Determine how many numbers I can put in the second digit..

I can also put  numbers in the second spot. Here's the reason why it's still :

Let's say I choose 2 for the first number. I will take  out of my set. I had numbers in my set..If i take a number out, I still have  numbers left. These numbers are: .

Step 4: Determine how many numbers I can put in the third and final digit...

I can put  numbers in the third slot..

I had  numbers at the start, and then I removed  of them. .

Step 5: Multiply how many numbers can go in the first, second, and third spot..

.

There are a total of  non-repetitive three-digit numbers that can be formed. 

Example Question #81 : Probability & Statistics

A coach of a baseball team needs to choose  players out of a total  players in the team. How many ways can the coach choose 9 players?

Possible Answers:

Correct answer:

Explanation:

Step 1: Recall the combination formula...

Step 2: Find  and  from the question..

.

Step 3: Plug in the values into the formula above..

Example Question #12 : Combinations

Six people run in a race, in how many different orders can they finish?

Possible Answers:

Correct answer:

Explanation:

This problem is solved by knowing that we have six options for first place, five options for second place, and so on.

Which means 

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