In a particular year, a company awards scholarships to 4 applicants from a group of applicants. If the order of selection is not taken into account, the number of ways in which the 4 scholarship recipients can be chosen is 7315.
- (i)
Find the number of ways in which the 4 scholarship recipients can be chosen if the order of selection is taken into account.
- (ii)
Find the value of .
In the year 2012, there are 13 scholarship applicants. The 13 applicants, which include the eventual 4 scholarship recipients Ann, Belle, Connie and Don, are required to attend a briefing. The applicants are to be seated in 2 rows as shown below:
Find the number of ways in which the 13 applicants can be seated if all 4 scholarship recipients must sit together during the briefing.
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Worked solution
7(i)
1. Relate the number of combinations to the number of permutations and evaluate
175,560
7(ii)
1. Formulate an equation for the number of ways to choose 4 recipients from $n$ applicants.
2. Solve for $n$ by testing integer values or using a graphing calculator.
Estimating since , we expect .
Testing integer values:
When ,
When ,
Hence, .
7[2]
1. Find the number of ways to position a contiguous block of 4 seats within the two rows.
The 4 scholarship recipients must sit together, so they must occupy 4 consecutive seats in the same row.
Number of valid blocks of 4 seats in the top row (6 seats)
Number of valid blocks of 4 seats in the bottom row (7 seats)
Total valid positions for the block
2. Formulate the total number of seating arrangements.
For each valid block position, the 4 scholarship recipients can be arranged among themselves in ways.
The remaining 9 applicants can be arranged in the remaining 9 seats in ways.
Total number of seating arrangements
3. Calculate the final value.
AI analysis — may contain mistakes.
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