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← JEE Main 2014 · 12 Apr · Shift 1
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JEE Main 2014 · 12 Apr · Shift 1, Mathematics question 66

8 - digit numbers are formed using the digits 1, 1, 2, 2, 2, 3, 4, 4. The number of such numbers in which the odd digits do not occupy odd places, is :

Choose one option
Answer and worked solution

Official answer: B

The odd digits 1, 1, 3 must sit in the 4 even places: (43)⋅3!2!=12\binom43\cdot\frac{3!}{2!}=12 ways.

The remaining 5 places take 2, 2, 2, 4, 4: 5!3! 2!=10\frac{5!}{3!\,2!}=10 ways. Total 120120.

Topics:Permutations
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