Ans is 100.......What's the catch here.....
See first 20 frames are being transmitted which has 0.8 chance off ariving undamaged......
so 20+20*0.8=20+16=36 frames arrived undamaged.....
now out of 16 also 0.8 are transmitted successfully......i.e; 16*0.8=12.8
therefore.....36+12.8=48.8
now for again 12.8 frames do the same thing......It's very hectic(It's for understanding)
so generally for n frames with p probability of transmitting undamaged is.....
n+np+np^2+p^3......
n(1+p+p^2+p^3.......)
n(1/(1-p)).....(infinite GP with a=1 and r=p)
now n=20 and p=0.8 given
so n(1/(1-p))=20/0.2=100
so 100 frames are transmitted....
