"Was that book interesting?"

Translation: その本は面白かったですか？

[dvkndn]

When to use かった and when to use い?

[StuartAuld]

かった is past tense, い is present

[Tordek]

Can you say ..i deshita?

[ForgetUmbrella]

It depends on whether the adjective is an い adjective or a な adjective.

い adjectives (which end in い, like おもしろい) must drop the い and add かった for the past tense (and use です). So おもしろい becomes おもしろかった.

On the other hand, な adjectives don't change, but use でした instead of です to signal past tense.

Note that な adjectives are adjectives that aren't い adjectives, but some な adjectives end in い, just like い adjectives, so you'll just need to memorise which is which, really.

[Tordek]

Thank you! That's a great explanation :)

[koumori72]

No.

[tonallyambiguous]

wait why would it be wrong if i said その本は面白かったんですか (including the ん before the ですか)

[JanniVV]

I'm guessing it's because it's a simple yes/no question, and んですか is used if you want an explanation rather than just a word answer.

[alltom]

Why does 面白い mean interesting here instead of funny? I just got several questions where it meant funny every time.

[Tordek]

You can also think about it as "amusing" or "entertaining".

[laxa88]

it can mean either funny or interesting. so, it depends on the context. :D

[deactivated user]

I feel that they should seperate the katta from the rest of the word, I was confused at first lol

[RayyanSheh1]

そのほんはおもしろかったですか?

Sono hon wa omoshiro katta desu ka?

[Nana.san]

1- 面白かった?
2- 面白いだった(の)?
3- 面白いだったんですか?
4- 面白かったんですか?
5- 面白いでしたか?

So many ways to say it~
The first two are not formal. The others. They actually don't use 2 and 3 so much.