the pattern goes like this
(6!/3!)-1 is divisible by7
but (8!/4!)-1 is not divisible by 9
but again (10!/5!)-1 is divisible by 11
then u might say that id denominator is odd it works
but even that is wrong
because (14!/7!)not divisible by 15
as far as i know the conditions for such a divisibility are as follows
1.denominator should be odd.eg 6!/3!
2.the number with u divide should be prime
since in the question asked we have 48! in the dr.(48 being even)
it is not divisible