Calculating multiple 'dice rolls'

[aboka]

hi, hv search online for howto calculate percentages for multiple dice rolls - we should use + if the event is 'once' and use x if they are inter-connect. for eg dice roll 1 has to be 5, and dice roll 2 must be 6. is that correct? and how about the example below?

sample#1
dice roll 1: 1/6
dice roll 2: 1/6
1/6 * 1/6 = 1/36 = 0.02777 x 100 = 2.777%

sample#2
stage 1: 1/2
stage 2: 1/10
stage 3: 1/10
stage 4: 1/24
1/2 * 1/10 * 1/10 * 1/24 = 1/4800 = 0.000208 x 100 = 0.0208%

sample#3
stage 1: 1/2
stage 2: 2/10
stage 3: 3/10
stage 4: 1/24
1/2 * 2/10 * 3/10 * 1/24 = 6/4800 = 0.00125 x 100 = 0.125%

thanks in advance.

cheers,