"想想看吧" can be translated into English as "Just think about it" or "Consider it", depending on the context and tone you want to convey.
"Just think about it" is more colloquial and commonly used in everyday conversations to encourage someone to ponder something.
"Consider it" is slightly more formal and can be used in situations where you want someone to give serious thought to a proposal or idea.
Both expressions effectively convey the meaning of urging someone to reflect or contemplate.