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6.Permutation and Combination
hard
From $6$ different novels and $3$ different dictionaries, $4$ novels and $1$ dictionary are to be selected and arranged in a row on a shelf so that the dictionary is always in the middle. The number of such arrangements is :
A
less than $500$
B
at least $500$ but less than $750$
C
atleast $1000$
D
at least $750$ but less than $1000$
(AIEEE-2009) (JEE MAIN-2018)
Solution
$\therefore $ Required number of ways ${ = ^6}{C_4}{ \times ^3}{C_1} \times 4!$
$ = 15 \times 3 \times 24 = 1080$
Standard 11
Mathematics