It happens to all of us at one time or another. Someone in the audience ask us a question about our presentation and we do not have the answer to it. What should we do?
The answer is clear: Just say “I don’t know.”
This is a much better strategy than to ham and haw and try to evade the question and give a non-responsive answer. All that bobbing and weaving is not going to do you one bit of good because the audience is doing to see right through you. So it is much better for you to just confess your ignorance AND ask if anyone in the audience has the answer.
In his seminal book “Moving Mountains”, Henry Boettinger says “quibbling and evasion produce disgust. If you don’t know the answer, say so directly.”