Do Protestants believe in the Triune God/the Holy Trinity?

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I attended Bible studies with a Protestant minister when I was in college, because there was lack of Bible studies for Catholics in my neighborhood - since I only live there for my studies. So the Pastor said that the Protestants' faith is solely based on the Bible. They interpret the Bible but, but only as good as its context allows it. That's why they don't believe that Mary was Assumed (Assumption) in Heaven. That's why they don't consider her Holy. However, I fail to see where the Trinity (Three Person in One God) is in the Bible. And based on what I understand, the Protestants believe the Trinity. I think this contradicts their faith. In the Catholic's perspective, we not only believe in the Word of God as embodied in the Bible but also in the Intelligence of Man in interpreting God's Word in some level - but never fully. That is the simplest way I can explain our belief of the Holy Trinity. What about the Protestants?