11N=9C1+.......9C8
only think about the position of 1.
it may take 2nd position to 9th.
for each of these select any 1,2,....8 nos. from (2,...10)& arrange them in their proper order.
so the ans is (b)
Let a1,a2,a3......,a10 be a permutation of the set {1,2,3......,10} such that the sequence ai decreases first and then increases like 8,6,4,1,2,3,5,7,9,10.If N is the number of such permutations,then the sum of digits of N is
a) 5 b) 6 c) 7 d) 9
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1 Answers
11