N3
わけだ
For that reason, No wonder, As you'd expect, Naturally, Thus, This is why
事故で電車が遅れたの?だから珍しく遅れて来たというわけだ。
The train was late due to an accident? So that's why you came in unusually late.
Explanation
「わけだ」 has 2 uses
1No wonder
Once you know the reason, the result makes sense, often with 「道理で」 or 「だから」: 「熱があるのか。苦しいわけだ」 (you have a fever? no wonder you feel bad).
雪が降っていた。寒い訳だ。
It snowed, so as you'd expect, it's cold.
指の骨が折れていたのですね。だから指を動かしたら痛かったという訳ですね。
You are saying that my finger was broken? So that's why my finger hurt when I moved it.
2So that means
Restates what came before as a conclusion or a sum: 「5%引きでポイントもつくなら、1割引きなわけだ」 (so it's really 10% off).
俺と一緒にいたくないわけだね?分かったよ。
So you are saying that you don't want to be with me, right? I understand.
先輩たちは後から来るというわけですか?
So the senpai are coming later?
Mixed up with
「わけだ」 no wonder; 「わけではない」 it's not that; 「わけがない」 there's no way; 「わけにはいかない」 I can't, for moral or social reasons.
「はずだ」 is a guess from evidence ('it should be so'), not yet confirmed. 「わけだ」 confirms a reason for something already known.