You purchased 100 shares of Amazon.com common stock on margin at $135 per share. Assume the initial margin is 0.65. You received a margin call when the share price dropped to $95. What is your maintenance margin requirement (MMR)?

Suppose you are holding a stock and there are three possible outcomes. The good state happens with 20% probability and 18% return. The neutral state happens with 55% probability and 9% return. The bad state happens with 25% probability and -5% return. What is the standard deviation of return?