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