Let X1, X2 and X3 be independent and identically distributed random variables with the uniform distribution on [0, 1]. The probability p{x1 is the largest} is
As X1, X2 and X3 are independent and identically distributed so P(x1)=P(x2)=P(x3)
So P(x1 is largest)=P(X2 is largest)=P(x3 is largest)
=13=0.33