Passed is both the past and past participle form of the verb pass. (Pass has many meanings, including to move, take place, go beyond, and complete successfully.)

Past is a noun (meaning "a previous time"), an adjective (meaning "ago"), and a preposition (meaning "beyond").

Examples:

• The past two weeks have been hard for Sally. She has not passed any of her exams. When she walked past me, I told her to forget the past and look toward the future.

• "We passed two men in baseball caps, chatting outside a pub."
  (Norman Lewis, "Essex")
• "I slithered across the mud in city clothes, past knots of bait-diggers forking worms into buckets."
  (Jonathan Raban, "Sea-Room")

Practice:

(a) We drove _____ the exit five minutes ago.

(b) We _____ the exit five minutes ago.

(c) In the _____, students wore caps and gowns.

(d) In _____ years, students had to do kitchen chores.

Answers to Practice Exercises

Glossary of Usage: Index of Commonly Confused Words