Here you go 3X

if 1-P(T) = .3

P(H)= .3

P(even numbers of head)= P(2H)+P(4H)+........+P(10)H

                                    =.09+.0081+.......

                                    = Approx    .1

I won't be surprised if some dhoti have asked such question. and as per your idea if they asked people to leave for such answers they will be end up with hiring crazy mathematicians only. The HR don't look for right answers instead they will look for how your attitude and your potential effort to answer those question.

By the way did anyone get call from quallcomm for the summer Intern.