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%.