"I'm jealous that maybe one of you gets to work on that," he added. "It's the juiciest problem ever."

"Today, I would go into software, which today that means going into artificial intelligence," the self-made billionaire said during a Q&A with Harvard students on Thursday. There are plenty of big, complex problems left to solve in the space, he says: "Computers still can't read. They cannot take a book of information and, say, pass an AP test on that book. And that's a solvable problem."

It's been 43 years since Bill Gates dropped out of Harvard University to co-found Microsoft . But if he found himself back on campus today, he knows exactly what he would choose to study: artificial intelligence.

Besides his passion for the topic, AI, Gates says, is "on the verge of making our lives more productive and creative."

"Think of all the time we spend manually organizing and performing mundane activities, from scheduling meetings to paying the bills," he writes in the foreword of Microsoft CEO Satya Nadella's book, "Hit Refresh."

"In the future, an AI agent will know that you are at work and have ten minutes free, and then help you accomplish something that is high on your to-do list."

It won't just boost productivity in the office, either, says Gates: "Innovation will improve many other areas of life too." It could help wipe out polio, for example. And "digital money is letting low-income users save, borrow, and transfer funds like never before."

If AI specifically doesn't interest you, Gates still encourages young people to consider science, engineering and economics. As he said during a Q&A with his wife Melinda and Lin-Manuel Miranda in New York City this year, "Clearly we need a hugely broad set of talents, but if your talents take you towards science or programming or advances in biology or energy breakthroughs, those kind of deep areas are going to be the biggest source of change."

There are multiple paths to success, he noted, but "if science grabs you … that is where a lot of the opportunity comes from. The more you can learn the science, the more you'll see where that next opportunity is."

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