What the !@#$? Only retards here? Not even the person who asked the question knows the right answer? I drew some %^-* to explain the math:

http://i.imgur.com/FSRQ0Xv.png

red circle: right portal

black circle: wrong portal

number next to circle: chance to get to that portal from the previous step

numbers in red circles are the outcomes how he could get the organ

chances:

1: (1/3*1/2)

2: (1/3*1/2)*(1/3*1/2)

3: (1/3*1/2)*(1/3*1/2)*(1/3*1/2)

4: (1/3*1/2)*(2/3)*(1/2*1/2)

5: (2/3)*(1/2*1/2)

6: (2/3)*(1/2*1/2)*(1/3*1/2)

7: (2/3)*(1/2)*(1*1/2)

so the total chance is 127/216=~56.8%

http://i.imgur.com/FSRQ0Xv.png

red circle: right portal

black circle: wrong portal

number next to circle: chance to get to that portal from the previous step

numbers in red circles are the outcomes how he could get the organ

chances:

1: (1/3*1/2)

2: (1/3*1/2)*(1/3*1/2)

3: (1/3*1/2)*(1/3*1/2)*(1/3*1/2)

4: (1/3*1/2)*(2/3)*(1/2*1/2)

5: (2/3)*(1/2*1/2)

6: (2/3)*(1/2*1/2)*(1/3*1/2)

7: (2/3)*(1/2)*(1*1/2)

so the total chance is 127/216=~56.8%