ok... i got it, sample space has 6^4 possibilities ; the number of possibilities for required event is 6 i.e. (1,1,1,1), (2,2,2,2),...,(6,6,6,6) ; so required prob= 6/6^4=1/6^3 ... thanks a lot! :)
_ _ _ _ these are the four places where we have to arrange no.s s.t no digit is repeated .
0,1,2,3,4,5,6,7,8,9.
In the thousand's place 0 can not come. So the remaining 9 can come in 9 ways.
Now out of the 10 no.s 1 no. is in the thousand's place ( anyone except 0)
remaining 9 nos. in 9 ways at the hundreds place.
then 8 no.s arranged in ten's place and 7 in one's.
Q73 9 options for first place excluding 0, 9 options for second place excluding the one occupying first place, similarly 8 options for third place and 7 for fourth.
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