The number of ways in which 10 candidates A1,A2,A3,A4....A10 can be ranked if A1 is just above A2, then the number of ways are
A
9!2!
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B
10!
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C
10!2!
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D
9!
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Solution
The correct option is D9! Once again taking A1A2 as a single block,
A1A2
A3
A4
A5
A6
A7
A8
A9
A10
We have 9 blocks to rank, hence, the no. of ways =9! However, A1A2 can not be switched this time, as A1 has to be ranked just above A2. So, the no. of ways in which the block rearranges itself is only 1! So. the total no. of ways =9!