Free Practice Question
PS · Problem Solving
705-805
Combinations
1 red flag, 3 white flags and 2 blue flags are arranged in a line such that: no two adjacent flags are of the same colour and the flags at the ends are of 2 different colours. In how many different ways the flags be arranged?
Answer Choices
Correct answer marked belowA
48
B
10
6
Correct
D
4
E
2
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Explanation
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Official Explanation
Official
The other approach is to think in terms of White: If there are 3 whites and they are never together - then out of 6, they will either take all odd places or all even places.
White in odd places: The other 3 remaining place will be taken by 1 Red and 2 Blue. So an arrangement of 3 with 2 things similar: …
White in odd places: The other 3 remaining place will be taken by 1 Red and 2 Blue. So an arrangement of 3 with 2 things similar: …
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What it tests
Whether you can count arrangements and selections correctly — permutations vs. combinations.
Common trap
Overcounting: treating a selection as ordered when order does not matter, or forgetting to divide by duplicates.
Details
Difficulty
705-805
Type
PS
Category