Combinations

Description: This quiz covers the fundamental concepts and applications of combinations in mathematics.
Number of Questions: 14
Created by:
Tags: combinatorics combinations counting probability
Attempted 0/14 Correct 0 Score 0

A club has 12 members. In how many ways can a president, vice-president, and secretary be chosen from the members?

  1. 1320

  2. 220

  3. 12

  4. 120


Correct Option: B
Explanation:

The number of ways to choose the president is 12. Once the president is chosen, the number of ways to choose the vice-president is 11. Finally, the number of ways to choose the secretary is 10. Therefore, the total number of ways to choose the president, vice-president, and secretary is 12 * 11 * 10 = 1320.

A box contains 6 red balls, 4 blue balls, and 2 green balls. In how many ways can 3 balls be selected from the box if at least one ball of each color is to be included?

  1. 168

  2. 120

  3. 96

  4. 80


Correct Option: C
Explanation:

First, select 1 red ball from 6 red balls, which can be done in 6 ways. Then, select 1 blue ball from 4 blue balls, which can be done in 4 ways. Finally, select 1 green ball from 2 green balls, which can be done in 2 ways. Therefore, the total number of ways to select 3 balls, one of each color, is 6 * 4 * 2 = 48. Since there are 3 different colors, there are 3 different ways to choose which color ball to select first. Therefore, the total number of ways to select 3 balls, at least one of each color, is 3 * 48 = 144.

A committee of 5 people is to be formed from a group of 10 people. In how many ways can this be done if 2 particular people must be included in the committee?

  1. 252

  2. 120

  3. 60

  4. 30


Correct Option: A
Explanation:

Since 2 particular people must be included in the committee, we need to choose 3 more people from the remaining 8 people. This can be done in 8C3 = 56 ways. Therefore, the total number of ways to form the committee is 56 * 2 = 112.

A bag contains 10 red marbles, 15 blue marbles, and 20 green marbles. In how many ways can 6 marbles be selected from the bag if there must be an equal number of red, blue, and green marbles?

  1. 560

  2. 280

  3. 140

  4. 70


Correct Option: B
Explanation:

Since there must be an equal number of red, blue, and green marbles, we need to select 2 marbles from each color. The number of ways to select 2 red marbles from 10 red marbles is 10C2 = 45. The number of ways to select 2 blue marbles from 15 blue marbles is 15C2 = 105. The number of ways to select 2 green marbles from 20 green marbles is 20C2 = 190. Therefore, the total number of ways to select 6 marbles, 2 of each color, is 45 * 105 * 190 = 891000.

A survey is conducted among 100 people to determine their favorite sport. The results show that 60 people like cricket, 40 people like football, and 20 people like both cricket and football. How many people like only cricket or only football?

  1. 80

  2. 60

  3. 40

  4. 20


Correct Option: A
Explanation:

Let C be the set of people who like cricket and F be the set of people who like football. Then, n(C) = 60, n(F) = 40, and n(C ∩ F) = 20. We want to find n(C ∪ F), which is the number of people who like either cricket or football. Using the inclusion-exclusion principle, we have: n(C ∪ F) = n(C) + n(F) - n(C ∩ F) = 60 + 40 - 20 = 80.

A company has 10 employees. In how many ways can a team of 3 employees be selected to attend a conference if 2 particular employees must be included in the team?

  1. 120

  2. 60

  3. 30

  4. 15


Correct Option: B
Explanation:

Since 2 particular employees must be included in the team, we need to choose 1 more employee from the remaining 8 employees. This can be done in 8C1 = 8 ways. Therefore, the total number of ways to select the team is 8 * 2 = 16.

A bag contains 6 red balls, 4 blue balls, and 2 green balls. In how many ways can 4 balls be selected from the bag if the selection must include at least 1 red ball and at least 1 blue ball?

  1. 240

  2. 120

  3. 60

  4. 30


Correct Option: A
Explanation:

First, select 1 red ball from 6 red balls, which can be done in 6 ways. Then, select 1 blue ball from 4 blue balls, which can be done in 4 ways. Now, we have 2 balls left to select, and we can choose either 2 green balls or 1 green ball and 1 red ball or 1 green ball and 1 blue ball. The number of ways to select 2 green balls from 2 green balls is 2C2 = 1. The number of ways to select 1 green ball and 1 red ball from 2 green balls and 5 red balls is 2C1 * 5C1 = 10. The number of ways to select 1 green ball and 1 blue ball from 2 green balls and 3 blue balls is 2C1 * 3C1 = 6. Therefore, the total number of ways to select 4 balls, including at least 1 red ball and at least 1 blue ball, is 6 * 4 * (1 + 10 + 6) = 240.

A club has 15 members. In how many ways can a president, vice-president, secretary, and treasurer be chosen from the members if the president cannot also be the vice-president?

  1. 13860

  2. 6930

  3. 3465

  4. 1732


Correct Option: B
Explanation:

First, select the president from 15 members, which can be done in 15 ways. Since the president cannot also be the vice-president, there are 14 members left to choose from. Select the vice-president from these 14 members, which can be done in 14 ways. Now, select the secretary from the remaining 13 members, which can be done in 13 ways. Finally, select the treasurer from the remaining 12 members, which can be done in 12 ways. Therefore, the total number of ways to choose the president, vice-president, secretary, and treasurer is 15 * 14 * 13 * 12 = 30030.

A committee of 5 people is to be formed from a group of 12 people. In how many ways can this be done if 3 particular people must be included in the committee?

  1. 220

  2. 110

  3. 55

  4. 28


Correct Option: A
Explanation:

Since 3 particular people must be included in the committee, we need to choose 2 more people from the remaining 9 people. This can be done in 9C2 = 36 ways. Therefore, the total number of ways to form the committee is 36 * 2 = 72.

A bag contains 10 red balls, 15 blue balls, and 20 green balls. In how many ways can 6 marbles be selected from the bag if there must be twice as many red marbles as blue marbles and three times as many green marbles as blue marbles?

  1. 140

  2. 70

  3. 35

  4. 17


Correct Option: B
Explanation:

Let x be the number of blue marbles to be selected. Then, the number of red marbles to be selected is 2x, and the number of green marbles to be selected is 3x. Since we are selecting a total of 6 marbles, we have x + 2x + 3x = 6, which gives x = 1. Therefore, we need to select 1 blue marble, 2 red marbles, and 3 green marbles. The number of ways to select 1 blue marble from 15 blue marbles is 15C1 = 15. The number of ways to select 2 red marbles from 10 red marbles is 10C2 = 45. The number of ways to select 3 green marbles from 20 green marbles is 20C3 = 1140. Therefore, the total number of ways to select 6 marbles, with twice as many red marbles as blue marbles and three times as many green marbles as blue marbles, is 15 * 45 * 1140 = 777000.

A group of 10 people is to be divided into two teams of 5 people each. In how many ways can this be done?

  1. 252

  2. 126

  3. 63

  4. 31


Correct Option: A
Explanation:

To divide the group into two teams of 5 people each, we can first choose 5 people for the first team from the 10 people. This can be done in 10C5 = 252 ways. Once the first team is chosen, the second team is automatically determined. Therefore, the total number of ways to divide the group into two teams of 5 people each is 252.

A club has 12 members. In how many ways can a president, vice-president, secretary, and treasurer be chosen from the members if the same person cannot hold more than one office?

  1. 924

  2. 462

  3. 231

  4. 115


Correct Option: B
Explanation:

First, select the president from 12 members, which can be done in 12 ways. Once the president is chosen, there are 11 members left to choose from. Select the vice-president from these 11 members, which can be done in 11 ways. Now, select the secretary from the remaining 10 members, which can be done in 10 ways. Finally, select the treasurer from the remaining 9 members, which can be done in 9 ways. Therefore, the total number of ways to choose the president, vice-president, secretary, and treasurer is 12 * 11 * 10 * 9 = 11880.

A bag contains 8 red balls, 6 blue balls, and 4 green balls. In how many ways can 6 balls be selected from the bag if there must be an equal number of red, blue, and green balls?

  1. 56

  2. 28

  3. 14

  4. 7


Correct Option: C
Explanation:

Since there must be an equal number of red, blue, and green balls, we need to select 2 balls from each color. The number of ways to select 2 red balls from 8 red balls is 8C2 = 28. The number of ways to select 2 blue balls from 6 blue balls is 6C2 = 15. The number of ways to select 2 green balls from 4 green balls is 4C2 = 6. Therefore, the total number of ways to select 6 balls, 2 of each color, is 28 * 15 * 6 = 2520.

A committee of 5 people is to be formed from a group of 10 people. In how many ways can this be done if 2 particular people must not be included in the committee?

  1. 252

  2. 126

  3. 63

  4. 31


Correct Option: C
Explanation:

Since 2 particular people must not be included in the committee, we need to choose 5 people from the remaining 8 people. This can be done in 8C5 = 56 ways. Therefore, the total number of ways to form the committee is 56.

- Hide questions