Last week, the director of the United Nation's World Food Programme said if the world's top billionaires just donated a fraction of their worth, millions of people who are at risk of starving to death can be saved. Elon Musk, the second wealthiest person in the world, said he'd give up some of his wealth – only if he knows exactly where the money is going. Musk, the founder of Tesla and SpaceX who has an estimated net worth of $151 billion, according to Forbes, replied to a tweet questioning the group's figures. "If WFP can describe on this Twitter...