SOLUTION: Three bolts and three nuts are in a box. Two parts are chosen at random. Find the probability that one is a bolt and one is a nut.

1.   In all, there are 3 + 3 =  6 different parts.

     Of them, you may form    =  = 15 different pairs of parts.



2.  From the other side, you have only  3*3 = 9  different pairs of the type (bolt,nut):  3 opportunities for bolts 

    and 3 independent opportunities for nuts.



3.  Therefore, the probability under the question is 


     = .


Answer.  The probability under the question is   = 0.6 = 60%.