머그컵과 초콜릿 관련 문장 해석 부탁드려요

“The mugs and the chocolate cost about the same, and in pretests students were as likely to choose one as the other.”
“Yet when offered the opportunity to switch from a mug to a chocolate bar or vice versa, only one in the switched.”
두 문장이 자연스럽게 해석되지 않네요.
도움 부탁드립니다~