8.04 Combinations

Evaluate the following expressions:

Prove the following:

Find the value of n if:

How many different unordered selections can be made from a set of 7 elements?

How many different unordered selections can be made from the set of letters of the Greek alphabet, which contains 24 letters?

Rewrite the following as a single factorial expression: \left(n - 1\right)! n \left(n + 1\right) for some positive whole number n.

Express the following without any factorial notation: \dfrac{\left(n + 2 + 5\right)!}{\left(n - 2\right)!} for some positive whole number n.

Ben has 3 shirts, each in a different colour: crimson (C), pink (P) and white (W), and 4 ties, each in a different colour: blue (B), grey (G), red (R) and yellow (Y).

A hotel is supervised by a team of 6 security guards at any given time during the day. If there are 12 security guards available, how many different ways can a team of guards be chosen?

A boss wants to select one group of 4 people from his 28 staff. How many different groups are possible?

A class of 28 students visit the tenpin bowling centre and must organise themselves into groups of 8 to use a lane. How many different ways are there for a group of 8 students to be formed?

A restaurant offers seven different sauces of spaghetti. Tricia chooses two sauces for her spaghetti. How many different possible choices could she make?

A variety pack of chocolate consists of seven bars, each with a different flavour. If three bars of chocolate are chosen at random, how many different selections are possible?

Out of the 16 cricket players, only 12 are selected for the team.

In a Lotto draw, 5 different numbers are chosen from the numbers 1 to 35. How many possible selections are there? Assume that order does not matter.

In court, a jury panel of 8 members is to be made up from a group of 20 candidates. In how many different ways can a panel be formed?

In a bicycle race, a quinella is a bet on the first 2 bicycles that finish the race, but the order in which these 2 bicycles place does not matter. How many different quinella bets are possible for a bicycle race where 14 bicycles are competing?

In a game of football, each team must have 1 goalkeeper and 10 other players on the field. A football squad consists of 17 players, 2 of which are goalkeepers. In how many ways can players be chosen to start the game?

A tea shop sells 10 different types of tea and 7 different sets of teacups, and has room to display 6 types of tea and 3 sets of teacups. The owner changes the display each month. How many different display combinations of tea and tea cups are possible?

A teacher wants to divide her 12 students into a group of 4, then a group of 5 and finally a group of 3. In how many ways can she do this?

Determine the number of ways 3 cards can be chosen from a standard deck of 52 cards if:

Amelia is playing a game of cards. She will randomly draw 5 cards from a standard deck of 52 cards, and wants only 3 of the cards to have clubs on them. How many different selections would contain the cards she wants?

Determine the number of ways 6 people can be chosen from a group of 11 people if:

10 red balls and 12 green balls are in a bag. 3 balls are to be selected from the bag at random, without replacement.

A selection of 4 people are to be chosen from a group of 7 people. How many selections are possible if the youngest or oldest is included but not both?

A team of 3 is to be chosen at random from a group of 5 girls and 6 boys. Determine the number of ways the team can be chosen if:

The state government needs to determine how school funding is allocated for the following year. Of the 8 public schools that will be affected, 5 of them are asked to attend a meeting. Determine the number of ways the 5 representative schools can be chosen if:

5 boys and 6 girls are part of the debate team. 4 of them must represent the school at the upcoming debate tournament. Determine the number of ways the team of 4 can be formed if:

A company has recently expanded overseas and is looking to recruit 5 new Resource Analysts. They have narrowed it down to 8 equally qualified applicants, of which 2 of them can speak a second language. In how many ways can they fill the positions if exactly one of the recruits must speak a second language?

In a court case, the defendant can choose a jury of 9 members from 15 candidates consisting of 9 women and 6 men. They notice that one particular lady looks ill and wish to avoid choosing her. How many different panels of jury members can they create if they want at least 7 women to make up the jury?

Yuri constructs 13 straight lines, no two of which are parallel. Three of the lines are concurrent (intersect at a single point). How many points of intersection are there?

In a radio discussion about an upcoming election, 7 Labour voters, 5 Liberal voters and 5 Greens voters called up to have a say. The radio announcers want to choose 1 Labour voter, at least 4 Liberal voters and at least 3 Greens voters to talk to on air. In how many ways can they select the callers?

A senior science teacher wants to receive feedback from a selection of students on whether they thought the exam was fair. The table shows the range of marks and the number of students who fell within each range:

She selects 2 students to provide feedback, but does not want more than 1 student from any score range. In how many ways can she select the 2 students?

Quiana is ordering a salad at a restaurant. She can order a salad consisting of just lettuce, or she can also add any of the following ingredients:

\text{Onions, Cucumbers, Tomatos, Cheese, Olives, Carrots, Mushrooms}

How many different variations of a salad can she possibly choose?

A company consists of 17 males and 12 females. 6 employees are selected at random without replacement.

A class of 24 students has 19 people whose birthday is in April. 4 students are selected at random without replacement.

A diagonal of a polygon is a line joining two non-adjacent vertices.