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    a fair coin is tossed repeatedly until a head appears or 3 tosses have been made. The random variablt T represents the number of tosses of the coin.

    a) Find the distrubution of T (3)
    b) Find the mean and standard deviation of T (5)
    c)Find the probability of obtaining exactly 3 tails on 2 successive attempts, (2)

    a discrete random variable x has the probability density function shown in the table below.

    x 0 1 2
    p(X=x) 1/3 a 2/3-a

    a) given that E(X) = 5/6, find the value of the constant a
    b) find the exact value of Var (x)
    c) Find the exact value of P(x lessthanor euqal to 1.5)
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    a is worth (3)
    b (4)
    c (1)
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    T can be 1,2 or 3.
    P(T=1) means a head must have be thrown, so P(T=1)=0.5
    Can you work out the other probabilities?

    b) you want E(T) and root of Var(T)...there are formulas given for these.
 
 
 
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