There are 7 colored flags: red, blue, yellow, green, purple, orange, and pink. These flags need to be hung in a row. The red flag must be in one of the first two positions, the purple flag and the orange flag cannot be adjacent, and the pink flag must be at the end. How many different arrangements are there?
Options
A
480
B
720
C
144
D
1,200
Answer & Analysis
Answer
C
Analysis
Question Analysis
This problem involves three constraints: fixed position for the pink flag, restricted positions for the red flag, and non-adjacent placement of purple and orange flags.
We solve it by breaking down each constraint step-by-step.
Key Concept Explanation
Fixed - position permutation: When an element has a fixed position (like the pink flag at the end), we reduce the number of elements to be permuted for the other positions.
Restricted - position permutation: For elements with restricted positions (the red flag in the first two positions), we calculate the number of ways to place them first.
Non - adjacency permutation: To handle non - adjacent elements (purple and orange flags), we use the method of finding the total arrangements without considering the non - adjacency and then subtracting the arrangements where they are adjacent.
Step - by - Step Solution
1. Place the pink flag:
Since the pink flag must be at the end, there is only 1 way to place it.
2. Place the red flag:
The red flag must be in one of the first two positions, so there are 2 ways to place the red flag.
3. Arrange the remaining 5 flags (excluding pink and the placed red flag) without considering the purple - orange non - adjacency:
The number of ways to arrange 5 flags is ways.
4. Calculate the number of arrangements where the purple and orange flags are adjacent:
Treat the purple and orange flags as one unit. The number of ways to arrange them within this unit is (purple - orange or orange - purple).
Then, considering this unit along with the other 3 non - red, non - pink, non - purple - orange flags, we have a total of 4 units to arrange. The number of ways to arrange these 4 units is ways.
So, the number of arrangements where the purple and orange flags are adjacent is
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