"It is an important investment."
Translation:C'est un investissement important.
'C'est un gros investissement' and 'C'est un investissement important' are given as correct, but 'C'est un important investissement' is marked wrong. Is this just Duolingo being inflexible or is it common practice to only use one- or two-syllable adjectives before the noun? ( Have to confess I put 'important' before the noun to see what would happen - it doesn't sound right.)
No, there is no rule related to the length of the adjective.
I suspect that for lack of available space, Duo tends to mix alternative translations with cross switches between this or that for ex, or his and her or synonymous adjectives, etc.
anyhow, in this example, putting the adjective "important" in front of the noun or after it does not change anything, except for the liaison:
- un important -T- investissement
- un investissement (no liaison) important