.8^9 - .8^19 The same thing was in a past paper, but I couldn't remember what to do with the indices so I just put .2(.8^9 + .8^10 ... + .8^19) in my calculator
I'm pretty sure it's right? I got that but wrote it as 0.0143
my first answer was 12/35 because i did something like (3C1 X 2C1 X 1C1 X 2C1)/7C4 and got 12/35. then i wanted to see if i got the same with another method and so i did 3/7 x 2/6 x 1/5 x 2/4 and got 1/70. so im not sure