A guess or shot in the dark made without solid basis; guesswork or speculation.
テストの最後の問題はわからなかったので当てずっぽうで答えを書いた。
I didn't know the last test question, so I wrote an answer by guessing.
当てずっぽうに番号を選んだら当たりが出た。
I picked a number at random and it turned out to be the winner.
当てずっぽうに聞いても正しい情報は得られない。
You won't get accurate information by asking randomly.