Binomial Coefficients

Description: This quiz covers the concept of binomial coefficients, which are used to calculate the number of ways to select a certain number of items from a larger set.
Number of Questions: 14
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Tags: combinatorics binomial coefficients pascal's triangle
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What is the formula for calculating the binomial coefficient of n and k, denoted as (\binom{n}{k})?

  1. $(\binom{n}{k} = \frac{n!}{k!})

  2. $(\binom{n}{k} = \frac{n!}{(n-k)!})

  3. $(\binom{n}{k} = \frac{(n+k)!}{n!})

  4. $(\binom{n}{k} = \frac{(n+k)!}{k!})


Correct Option:
Explanation:

The binomial coefficient (\binom{n}{k}) represents the number of ways to choose k items from a set of n distinct items, without regard to order. The formula (\binom{n}{k} = \frac{n!}{k!(n-k)!}) is derived from the fundamental principle of counting.

What is the value of (\binom{5}{2})?

  1. 10

  2. 15

  3. 20

  4. 25


Correct Option: A
Explanation:

Using the formula (\binom{n}{k} = \frac{n!}{k!(n-k)!}), we can calculate (\binom{5}{2} = \frac{5!}{2!(5-2)!} = \frac{5!}{2!3!} = \frac{120}{2\cdot6} = 10).

What is the relationship between binomial coefficients and Pascal's Triangle?

  1. The entries in Pascal's Triangle are equal to binomial coefficients.

  2. The entries in Pascal's Triangle are the sums of binomial coefficients.

  3. The entries in Pascal's Triangle are the differences of binomial coefficients.

  4. The entries in Pascal's Triangle are the products of binomial coefficients.


Correct Option: A
Explanation:

Pascal's Triangle is a triangular array of binomial coefficients, where each entry is the sum of the two entries above it. The first row of Pascal's Triangle consists of 1, the second row consists of 1 and 1, and so on.

Which of the following identities involving binomial coefficients is known as Pascal's Identity?

  1. $(\binom{n}{k} = \binom{n-1}{k} + \binom{n-1}{k-1})

  2. $(\binom{n}{k} = \binom{n}{n-k})

  3. $(\binom{n}{k} = \frac{n!}{k!})

  4. $(\binom{n}{k} = \frac{n!}{(n-k)!})


Correct Option: A
Explanation:

Pascal's Identity states that the binomial coefficient (\binom{n}{k}) can be expressed as the sum of the two binomial coefficients (\binom{n-1}{k}) and (\binom{n-1}{k-1}). This identity is fundamental in the study of binomial coefficients and has various applications in combinatorics.

What is the coefficient of (x^3) in the expansion of ((1+x)^{10})?

  1. 120

  2. 252

  3. 495

  4. 792


Correct Option: A
Explanation:

Using the binomial theorem, we can expand ((1+x)^{10}) as (\sum_{k=0}^{10} \binom{10}{k} x^k). The coefficient of (x^3) corresponds to (k=3), so we have (\binom{10}{3} = \frac{10!}{3!7!} = \frac{10\cdot9\cdot8}{3\cdot2\cdot1} = 120).

How many ways can 6 people be divided into two groups of 3 people each?

  1. 20

  2. 30

  3. 40

  4. 50


Correct Option: A
Explanation:

To solve this problem, we can use the binomial coefficient (\binom{n}{k}). In this case, we have n = 6 (total number of people) and k = 3 (number of people in each group). So, the number of ways to divide 6 people into two groups of 3 people each is (\binom{6}{3} = \frac{6!}{3!3!} = \frac{6\cdot5\cdot4}{3\cdot2\cdot1} = 20).

What is the coefficient of (x^5) in the expansion of ((2x-3)^{8})?

  1. 1344

  2. 2016

  3. 2720

  4. 3584


Correct Option: C
Explanation:

Using the binomial theorem, we can expand ((2x-3)^{8}) as (\sum_{k=0}^{8} \binom{8}{k} (2x)^{8-k}(-3)^k). The coefficient of (x^5) corresponds to (k=3), so we have (\binom{8}{3} (2)^{8-3}(-3)^3 = \frac{8!}{3!5!} \cdot 2^5 \cdot (-3)^3 = 2720).

In a class of 30 students, how many ways can a teacher select 5 students to participate in a debate competition?

  1. 142506

  2. 2598960

  3. 1454928

  4. 15504


Correct Option: A
Explanation:

To solve this problem, we can use the binomial coefficient (\binom{n}{k}). In this case, we have n = 30 (total number of students) and k = 5 (number of students to be selected). So, the number of ways to select 5 students from a class of 30 students is (\binom{30}{5} = \frac{30!}{5!25!} = \frac{30\cdot29\cdot28\cdot27\cdot26}{5\cdot4\cdot3\cdot2\cdot1} = 142506).

What is the value of (\binom{100}{99})?

  1. 99

  2. 100

  3. 101

  4. 102


Correct Option: B
Explanation:

Using the property (\binom{n}{k} = \binom{n}{n-k}), we can simplify (\binom{100}{99}) as (\binom{100}{100-99} = \binom{100}{1} = 100).

In a group of 12 people, how many ways can a committee of 4 people be formed if 2 specific people must be included in the committee?

  1. 330

  2. 495

  3. 660

  4. 792


Correct Option: A
Explanation:

Since 2 specific people must be included in the committee, we need to select 2 more people from the remaining 10 people. So, the number of ways to form the committee is (\binom{10}{2} = \frac{10!}{2!8!} = \frac{10\cdot9}{2\cdot1} = 45). However, since the 2 specific people can be arranged in 2 different orders, we need to multiply this value by 2. Therefore, the total number of ways to form the committee is 2 (\cdot) 45 = 90.

What is the coefficient of (x^6) in the expansion of ((x+2)^{12})?

  1. 924

  2. 1716

  3. 2772

  4. 3003


Correct Option: A
Explanation:

Using the binomial theorem, we can expand ((x+2)^{12}) as (\sum_{k=0}^{12} \binom{12}{k} x^{12-k}2^k). The coefficient of (x^6) corresponds to (k=6), so we have (\binom{12}{6} 2^6 = \frac{12!}{6!6!} \cdot 2^6 = \frac{12\cdot11\cdot10\cdot9\cdot8\cdot7}{6\cdot5\cdot4\cdot3\cdot2\cdot1} \cdot 64 = 924).

In a survey, 100 people were asked about their favorite sports. 60 people said they liked soccer, 40 people said they liked basketball, and 20 people said they liked both soccer and basketball. How many people liked only soccer or only basketball?

  1. 60

  2. 80

  3. 100

  4. 120


Correct Option: C
Explanation:

Let (S) be the set of people who liked soccer, (B) be the set of people who liked basketball, and (S\cap B) be the set of people who liked both soccer and basketball. Then, by the principle of inclusion-exclusion, the number of people who liked only soccer or only basketball is (|S\cup B| = |S| + |B| - |S\cap B| = 60 + 40 - 20 = 80).

What is the coefficient of (x^4) in the expansion of ((3x^2-2)^{6})?

  1. 432

  2. 864

  3. 1296

  4. 1728


Correct Option: C
Explanation:

Using the binomial theorem, we can expand ((3x^2-2)^{6}) as (\sum_{k=0}^{6} \binom{6}{k} (3x^2)^{6-k}(-2)^k). The coefficient of (x^4) corresponds to (k=2), so we have (\binom{6}{2} (3x^2)^{6-2}(-2)^2 = \frac{6!}{2!4!} \cdot 3^4x^8 \cdot 4 = 1296x^8).

How many ways can a club of 15 members select a president, a vice president, and a secretary?

  1. 2730

  2. 32760

  3. 40950

  4. 48620


Correct Option: A
Explanation:

To solve this problem, we can use the multiplication principle. First, the club can select a president in 15 ways. Then, the club can select a vice president from the remaining 14 members in 14 ways. Finally, the club can select a secretary from the remaining 13 members in 13 ways. Therefore, the total number of ways to select a president, a vice president, and a secretary is 15 (\cdot) 14 (\cdot) 13 = 2730.

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