i) find k such that Pk+1/Pk>1
ii) Pn=2nCn(0.5)n(0.5)2n-n=2nCn(0.5)2n
simplify
iii) is attached
edit: ok i made a mistake; in the 4th line of working i factored out 22n four times => i should have factored out 2n four times because their are n 2's and not 2n 2's
hence, this gets rid of the spare 24n and so disregard the second last line