http://i45.tinypic.com/2wburdd.jpg

member 1 is exponential of lambda=1 X1~exp(3)
member 2 is U(2,4) X2~U(2,4)
member 3 works 3 hours and then dont work at all
X3=1 for t<3
X3=0 for t>3
<br />
F_{X_{ab}}(t)=P(x_b<t)=p(max(x_1,x_{23})<t)=P(x_1<  t)P(x_{23}<t)\\<br />
=P(x_1<t)P(min(x_2,x_{3})<t)
i developed it at much as i could
i dont know how to continue from this point
to find the formula