Here's a breakdown of all possible scenarios after you picked A. I figure there is a 33% chance of each answer being right before a wrong answer is revealed, and the teacher won't eliminate the correct answer but has a 50% chance of eliminating each wrong answer. I included all the possible wrong answers the teacher could have eliminated. Notice that all of the scenarios have equal chance of happening, and in 2 of the 6 scenarios you would be right, in 2 you would be wrong, and in 2 you would need to switch your answer. In a case where after the teacher eliminates an answer you didn't pick, you have a 1/2 chance of being right. If the teacher had eliminated the number you already picked, you switch and still have a 1/2 chance of being right.

• • 1. You guess A. Correct Answer is A (33% chance). Teacher eliminates A (0% chance). You are right (0% chance).
  • 2. You guess A. Correct Answer is A (33% chance). Teacher eliminates B (50% chance). You are right (16.67% chance).
  • 3. You guess A. Correct Answer is A(33% chance). Teacher eliminates C (50% chance). You are right (16.67% chance).
  • 4. You guess A. Correct Answer is B (33% chance). Teacher eliminates A (50% chance). You need to switch (16.67% chance).
  • 5. You guess A. Correct Answer is B (33% chance). Teacher eliminates B (0% chance). You are wrong (0% chance).
  • 6. You guess A. Correct Answer is B (33% chance). Teacher eliminates C (50% chance). You are wrong (16.67% chance).
  • 7. You guess A. Correct Answer is C (33% chance). Teacher eliminates A (50% chance). You need to switch (16.67% chance).
  • 8. You guess A. Correct Answer is C (33% chance). Teacher eliminates B (50% chance). You are wrong (16.67% chance).
  • 9. You guess A. Correct Answer is C (33% chance). Teacher eliminates C (0% chance). You are wrong (0% chance).

In the Monty Hall scenario, teacher would never eliminate the answer you selected. Instead of a 50/50 chance of eliminating what you had already selected, the teacher would always eliminate the other option if your choice is wrong. This changes the chance of each outcome happening, doubling some and eliminating others leaving you with a 1/3 chance of being right with the option you had picked, but a 2/3 chance of being right if you had switched.

• 1. You guess A. Correct Answer is A (33% chance). Teacher eliminates A (0% chance). You are right (0% chance).
• 2. You guess A. Correct Answer is A (33% chance). Teacher eliminates B (50% chance). You are right (16.67% chance).
• 3. You guess A. Correct Answer is A(33% chance). Teacher eliminates C (50% chance). You are right (16.67% chance).
• 4. You guess A. Correct Answer is B (33% chance). Teacher eliminates A (0% chance). You need to switch (0% chance).
• 5. You guess A. Correct Answer is B (33% chance). Teacher eliminates B (0% chance). You are wrong (0% chance).
• 6. You guess A. Correct Answer is B (33% chance). Teacher eliminates C (100% chance). You are wrong (33.33% chance).
• 7. You guess A. Correct Answer is C (33% chance). Teacher eliminates A (0% chance). You need to switch (0% chance).
• 8. You guess A. Correct Answer is C (33% chance). Teacher eliminates B (100% chance). You are wrong (33.33% chance).
• 9. You guess A. Correct Answer is C (33% chance). Teacher eliminates C (0% chance). You are wrong (0% chance).

Edited for formatting and to add the options with a 0% chance of happening.