How many ways are there to assign 5 different jobs to 4 different employees if…
2021
How many ways are there to assign 5 different jobs to 4 different employees if every employee is assigned at least 1 job?
- A.
1024
- B.
625
- C.
240
- D.
20
Attempted by 231 students.
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Correct answer: C
Answer: 240 ways.
Method 1 (Inclusion–Exclusion):
Total assignments without restrictions: 4^5 = 1024.
Use inclusion–exclusion to remove assignments that leave one or more employees with zero jobs.
4^5 - C(4,1)·3^5 + C(4,2)·2^5 - C(4,3)·1^5 = 1024 - 4·243 + 6·32 - 4·1 = 240.
Method 2 (Stirling numbers):
Number of ways to partition 5 distinct jobs into 4 nonempty unlabeled groups is S(5,4) = 10.
Label the 4 groups by the 4 distinct employees: multiply by 4! = 24, giving 10·24 = 240.
Both methods agree, so the number of ways is 240.
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