To Confuse, To Mistake
Transitive verb and Ichidan verb
まちがえる
こんな簡単な問題を間違えるなんて、悔しいよ。
Making a mistake on such a simple question is so frustrating.
Remember how 間違い means "a mistake?" Well this is the verb version. It means to make a mistake.
It's read the same as 間違い! Nice and easy!