Your did not give "I do not know" as a choice. I would not be surprised that people do not know how much leverage they use.
No margin ever. I always use (and recommend to use) leveraged ETFs, so you have staying power and never will get margin calls. Brokers bash leveraged ETFs because they can't charge margin interests and they don't get the stop-loss commissions.
I have answered this (40%) assuming the following formula: amount borrowed on margin against assets = (total asset value - equity value)/(total asset value) Is this correct, and what you intended? I autotrade stocks/ETFs intraday, and my broker allows me to borrow (assuming the above formula) up to 75% on margin against assets.