consider seven digit numbers x1 x2 .... x7 ≠0 having the prop that x4 is the greatest digit and the digit to left and right of x4 are in decreasing order then total number of such numbers in which all the digits are distinct is....???
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2 Answers
62first we have to chose 7 distinct numbers from 1 to 9
that can be done in 9C2 ways
NOw the largest is fixed at x4
frmo the remaining 6, make 2 partitions of 3 each ...
each will give one way... to find x1,x2, x3
thus
no of ways is
9C2. x 6C3