Hi cgiulz.

There are 3 cylinders on the left side and 3 cylinders on the right side.

firing a cylinder on the right side, there are 3 possibilities. After that you have to fire one on the left side. there are 3 possibilities, too.

Now you are back on the right side, there are 2 possibilities (because one cylinder already is fired) - on the left side there are 2 possibilities.

Therefore

Probability("firing right, firing left, firing right, left, right left") = 3*3*2*2*1*1

I guess you can start firing a cylinder on the left side, too, therefore

Probability("firing left, right, left right left, right= 3*3*2*2*1*1

and the solution therefore is

2*(3*3*2*2*1*1)

Do you have any thoughts on (b) now?

Rapha