@JTT,
Well, I think you are expecting answers in which I should express possibility simply by modals. However, many other things were also mentioned, in this topic, too, so I tried to write (at least) two sentences in every required situation. The first one is the one I would say normally (it’s the way how it is most natural for me), without any special requirement, and in the other I tried to say something similar simply by a modal. Besides, writing the second sentences, I’ve also used your guideline about percents, however it doesn’t means rejecting contrary opinions, like Monterey Jack’s one. I guess English has many spoken versions and you may prefer different versions. But now I remain at your English, because it may be very much or lesser general, but it’s much more general than my English which is spoken only by me. However, I think the first sentences are better, because they’re based on my total experience, on the whole of my observations.
/1. KaJe, you are 10% certain that John is going to go to Moscow this Saturday./
a)It may happen that John will go to Moscow on Saturday.
b)It may happen that John will go to Moscow on Saturday.
/2. You [KaJe] are 95% certain that Mary likes pizza./
a)It’s very likely that Mary likes pizza. OR: I think Mary likes pizza.
b)Mary must like pizza.
/3. You are 40% certain that Albert lives in Mexico City./
a)It is possible that Albert lives in Mexico City.
b)Albert may live in Mexico City.
/4. You are 75% certain that Gene doesn't work for Toyota./
a)It’s not probable that Gene works for Toyota. OR: I don’t really think that Gene works for T.
b) [Well, “should”/”shouldn’t” don’t seem to be proper now, so no answer of that kind.]
/5. You think it's possible that Martha is at home right now./
a)Martha may at home now.
b)Martha may at home now.
/6. You are 23% certain that Nancy ate spaghetti for lunch./
a)It might be that Nancy ate spaghetti for lunch.
b)Nancy might have eaten spaghetti for lunch.
/7. You are 65% certain that Joan used to be married to Jack./
a)It’s possible that Joan used to be married to Jack.
b)[no answer with modal]
/8. You are 20% certain that Frank died in 1975./
a)Frank might have died in 1975.
b)Frank might have died in 1975.
/9. You are 10% certain that Jillian wanted to go with everyone to the beach./
a)It’s not possible that Jillan wants to go with everyone to the beach. OR: It’d doubtful that…
b)Jillian might not want to go with everyone to the beach.
/10. You are 45% certain that Greg bought wine for the party./
a)It may be that Greg bought wine for the party.
b)Greg may have bought wine for the party.