Say you don’t know the answer when you don’t know the answer. (Footnote 1)
Footnote 1 From Reddit:
I hire quite a bit and my biggest red flag is people who profess to know the answer to every question and never admit to not knowing something. I have a couple of really-too-advanced-for-the-role technical questions that I keep in my back pocket and use almost entirely to see what people will say when they DON’T know the answer. Being able to tell me how you find out information you don’t know (and showing me that you don’t mind admitting not being perfect/asking questions) is WAY more valuable than “acing” an interview quiz.
(This is also one of the most valuable traits of an employee – if you don’t know something/screw up, admitting it will win you WAY more points than you trying to hide it/cover your tracks. Coming clean about a screwup – assuming it’s not a habit, obviously – shows me you are both honest and confident.)