Questions
The number of ways in which we can arrange the digits 1, 2, 3, …, 9 such that the product of five digits at any of the five consecutive positions is divisible by 7 is
detailed solution
Correct option is C
Let an arrangement of 9 digit number be x1x2x3x4x5x6x7x8x9.Note that we require product of each of x1,x2,x3,x4,x5;x2,x3,x4,x5,x6;…;x5,x6,x7,x8,x9 is divisible by 7.This is possible if the 5th digit is 7.Therefore, we can arrange the 9 digits in desired number of ways in 8! ways.Similar Questions
The number of ways in which we can get at least 6 successive tails when a coin is tossed 10 times in a row, is
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