Question

A random variable X has the probability distribution

value 1 2 3 4

probability 0.5 0.25 0.125 0.125

(For those of you who are interested, this is the geometric p=0.5 “killed” at 4. X is the number of times I toss a coin if I follow this rule: I’ll toss the coin till I get the first head, but I’ll stop after 4 tosses even if I haven’t got a head by that time.) Find E(x)

Answer 1

E(x)=1.875 - this correct

Explanation ( E(X) = (1*0.5)+(2*0.25)+(3*0.125+(4*0.125)=1.875 )

Answer 2

if somebody interesting in SE(X) ... ;-)

SE(X)=1.053268
Explanation ( sqrt(((1-1.875)^2)*0.5+((2-1.875)^2)*0.25+((3-1.875)^2)*0.125+((4-1.875)^2)*0.125) )

dont foget to say "thanks" or pres "Best Responce"