Permutation and CombinationHard

Question

Number of natural number upto one lakh, which contains 1,2,3,  exactly once and remaining digits any time is -

Options

A.2940
B.2850
C.2775
D.2680

Solution

First fill 3 places by 1,2,3 in ways and then remaining one in 7 × 7 ways  so total no. of ways
=  5P3 × 7 × 7 = 2940

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