In a Reddit “Ask Me Anything” Monday, Bill Gates solicited questions from the internet and answered dozens of them, from serious questions about the future of philanthropy to silly ones about his favorite prime number (it’s 2).

Gates, the founder of Microsoft and for many years the richest man in the world, has along with his wife given away more than $35 billion through the Bill and Melinda Gates Foundation. They plan to give away nearly all of their wealth.

Reddit AMAs are a popular way for celebrities, politicians, and anyone who’s had an unusual or exciting experience to reach a big audience. Obama did one, as did Trump. Gates particularly likes the format — he’s done seven.

Like it or not — and in a political environment increasingly hostile to billionaires and skeptical of big-dollar philanthropy, more people are voicing their reservations about it — Gates’s thinking on the world’s top priorities is incredibly important. His foundation is one of the biggest private contributors to work on global health. The Gates Foundation spends more on global health each year than most countries. Their work has saved millions of lives. Gates inevitably features front and center as we wrestle with the role of billionaires in the world.

Here’s a roundup of eight of the most interesting questions and answers yesterday, including Gates’s thoughts on charity, his goals for the Gates Foundation, and the lives and role of the ultra-wealthy.

1) On the Gates Foundation and his goals for global health

Question from Swcomisac: “What would you still like to achieve that you haven’t?”

Gates: “The goal of the Foundation is that all kids grow up healthy — no matter where they are born. That means getting rid of malaria and many of the other diseases that affect poor countries. It should be achievable in my lifetime.”

2) On the amazing progress we’ve made so far in global health

Question from KubrickIsMyCopilot: “What’s the most encouraging bit of progress your foundation has funded to date?

Gates: “Our biggest achievement is working with partners (including rich government aid groups like USAID and DFID) to make sure all the children in the world get vaccines. This is a big part of the reason that deaths of children under 5 has dropped from over 10M when we started to less than 6M now. GAVI is the name of the group that was created — all the donors to GAVI deserve huge thanks (mostly from the voters in the countries who gave).”

3) On technology that could change the world

Question from ironsheik84: “What’s a piece of technology that’s theoretical now that you wish you could make possible immediately? Thanks in advance and thank you for all of your humanitarian efforts!”

Gates: “I am fascinated by how hard it has been to teach computers to actually read so they understand the material. An example would be reading a textbook and passing a test. This question of knowledge representation is a fascinating one that Microsoft and lots of others are working on.

“However, if I had one wish to make a new technology it would be a solution to malnutrition. Almost half the kids in poor countries grow up without their body or brain developing fully so they miss most of their potential.

“Second would be an HIV vaccine.”

4) On the biggest risks to humanity

Question from Realhuman221: “What do you think the greatest threat to humanity is at this moment?”

Gates: “There are some things that aren’t likely but we should worry about — nuclear bombs and bioterrorism (from nation states or terrorism), or a big pandemic. This is the 100th anniversary of the Spanish flu [which killed 50 million people] and if it came back the amount of travel would make it spread faster than it did last time.

“Once you get past those threats then the biggest question is global cooperation to avoid climate change and reduce the risk of war. It is disconcerting to see a rise of countries turning inwards and not investing in alliances which have helped us avoid big wars since World War II.

“Climate change is a real test of how we can work together globally since it is a complex problem where major changes need to be done well in advance of the big harms.”

5) On how much he should pay in taxes

Question from habituallinestepper1: “What do you think you, personally, should be paying in taxes each year?”

Gates: “I think our system can be a lot more progressive (that is richer people paying a higher share).

“A key element is making capital gains taxation more like ordinary income (some have suggested making them the same) and having an estate tax more like we had in the past (55% above $3.5M).

“European countries collect a lot more taxes but through consumption taxes, but those are not progressive.

“If people want the government to do more it needs to be funded and I see us needing to improve our education and health services.

“So yes, I have paid $10B but I should have had to pay more on my capital gains.”

6) On how to combat billionaire tax avoidance

Question from PJHart86: “Hi Bill, what do you think about Rutger Bregman’s recent comments at Davos? is it even possible for governments to compel billionaires to pay their fair share of taxes, even if they wanted to?”

Gates: “As far as I know, most billionaires (and other people) comply with tax laws. There should be more transparency so it is clear who [owes] what and how loopholes are reducing tax collection. Countries need to work with each other on this.

“It is pretty amazing how few countries have estate taxes — even China doesn’t have one.”

7) On what it’s like to be a billionaire

Question from vansebastian: “The internet is fascinated by seeing you do ‘normal’ things, like wait in line for a burger. But what’s the most ‘treat yo self’ rich-guy thing that you do?”

Gates: “I have a nice house. It includes a trampoline room which seems kind of over the top but my kids love using it to work off their excess energy. I am not sure how guilty I should feel about being in a great house.

“The other thing is that I sometimes use a private jet. It does help me do my foundation work, but again it is a very privileged thing to have.”

8) On whether money really does buy happiness

Question from DanielAyon: “Do you think being a billionaire has made you a happier person than if you were just a middle-class person?”

Gates: “Yes. I don’t have to think about health costs or college costs. Being free from worry about financial things is a real blessing. Of course you don’t need a billion to get to that point. We do need to reduce the cost growth in these areas so they are accessible to everyone.”

You can read the full AMA here.

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