SATHEE: Permutations And Combinations Question 273

Permutations And Combinations Question 273

Question: The number of numbers that can be formed with the help of the digits 1, 2, 3, 4, 3, 2, 1 so that odd digits always occupy odd places, is [RPET 1988, 1991, 1992]

Options:

A) 24

B) 18

C) 12

D) 30

Show Answer

Answer:

Correct Answer: B

Solution:

The 4 odd digits 1, 3, 3, 1 can be arranged in the 4 odd places in $ \frac{4\ !}{2\ !\ 2\ !}=6 $ ways and 3 even digits 2, 4, 2 can be arranged in the three even places in $ \frac{3\ !}{2\ !}=3 $ ways. Hence the required number of ways $ =6\times 3=18 $ .

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Permutations And Combinations Question 273

Question: The number of numbers that can be formed with the help of the digits 1, 2, 3, 4, 3, 2, 1 so that odd digits always occupy odd places, is [RPET 1988, 1991, 1992]

Options:

Answer:

Solution:

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