The number of different seven digit numbers that can be written using only the three digits 1, 2 and 3 with the condition that the digit 2 occurs exactly twice in each number is
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a
7P2 . 25
b
7C2 . 25
c
7C2 . 52
d
7C2 . 10
answer is B.
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Detailed Solution
We have to select 2 places for the digit 2. This can be done in7c2 ways Remaining each place can be filled in 2 ways(1,3) =7c2.25
The number of different seven digit numbers that can be written using only the three digits 1, 2 and 3 with the condition that the digit 2 occurs exactly twice in each number is