Question 1021562
1.  The r.v. X (the number of premium buses) follows the Binomial distribution. Here, x = 0,1,2,3,4,5,6,7,8,9,10.
{{{p(x) = C(10,x)(4/5)^(10-x)(1/5)^x}}}

2.  The expected value of the r.v. X (the number of premium buses) is {{{np = 10*(1/5) = 2}}}.

3.  The variance of X is {{{np(1-p) = 10*(1/5)*(4/5) = 1.6}}}

4.  The answer is p(6)+p(7)+p(8)+p(9)+ p(10).  Now just use p(x) from no.1 and your scientific calculator to find the pertinent probability. (0.00637)