Say, If 3 Canons, A, B, C, Have The Probability Of Hitting Their Targets, 0.5, 0.33, 0.25 Respectivly How Would I Calculate The Probability Of:

a. None Of Them Hitting.

b. Exactly One Of Them Hitting.

c. Exactly Two of Them Hitting.

I Have Tried Different Approaches, Each Giving Me Strange Results, So Please Help