So how would you say "These are the right decisions". Ce sont les bonnes decisions? (Just a guess)
Would "these are some good decisions" not also be correct? This was marked wrong when I tried it.
You may have understood that "des" means "some". But it is really just the plural of "un" or "une". There is no actual equivalent for this word in English although some people use "some". Remember that in English, "some" is usually understood as "a few" which would be "quelque(s)", i.e., un peu de, n'importe quel. So there really is a difference. Take a look here: http://www.larousse.fr/dictionnaires/francais-anglais/quelque/664448
Like pakjim I'm also confused. In the singular construction it is "right", but in the plural it is "good". Please explain.
I think we need les bonnes décisions instead of des. Des signifies part of the decisions are right (or good), rather than all of the right decisions.
In English, you wouldn't say "these are right decisions" (Ce sont de bonnes décisions). You would instead say "these are the right decisions" (= ce sont les bonnes décisions).
"Ce sont de bonnes décisions" (these are good decisions) is the plural of "c'est une bonne décision" (this is a good decision).
"Ce sont les bonnes décisions" (these are the good decisions) is about specific decisions.
To get "les bonnes décisions" as a generalization, you would need another type of sentence, like "les bonnes décisions sont difficiles à prendre" = good decision are difficult to make.