Question 1116213
You are multiplying, so you don't need a common factor:
(99/100)*(80/81)*(63/64)*(48/49)*(35/36)*(24/25)*(15/16)*(8/9)*(3/4)
= (99*80*63*48*35*24*15*8*3)/(100*81*64*49*36*25*16*9*4) = 11/20