We know that,
odd no. + odd no.= even no.
_ + _ + _ + _ + _ =30
therefore, upto 4 blanks, the no. formed will be even.
even no. + _ = even no. (30 is even no.)
_ = even no.-even no.
_ = even no.
this is not possible since, we cannot fill blanks with even no.s
hence, we cannot fill all five blanks with odd no.s to get 30.