Q.

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

see full answer

Start JEE / NEET / Foundation preparation at rupees 99/day !!

21% of IItians & 23% of AIIMS delhi doctors are from Sri Chaitanya institute !!
An Intiative by Sri Chaitanya

a

8!

b

5(7!)

c

 9P7

d

7!

answer is C.

(Unlock A.I Detailed Solution for FREE)

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Detailed Solution

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.

Watch 3-min video & get full concept clarity

tricks from toppers of Infinity Learn

score_test_img

Get Expert Academic Guidance – Connect with a Counselor Today!

whats app icon