From Reuters Alert Net, writer Katie Nguyen attended the presentation.
"When money is spent wisely, it saves lives, it improves livelihoods and it builds prosperous societies. Bill and I think when you find a leverage point that is this powerful, you should take advantage of it. When we find a way to save millions of lives, we should do more of it. When find a way to improve hundreds of millions of lives, we should give it all we've got," Melinda Gates told an audience of development experts, academics and celebrities.
"So when it comes to development we are both optimists."
The couple are spreading the word through "Living Proof", a campaign to "bust the myths" and highlight what they consider is working well in development.
Taking it in turns to speak, they pressed home their point with slick graphs, photos and video of successful vaccination, maternal health and agricultural programmes from Nicaragua to Ethiopia and Tanzania.
Melinda Gates said that, since 2003, Ethiopia has opened 15,000 remote healthcare clinics and trained 35,000 healthcare workers. The number of mothers who have received two prenatal visits has doubled since 2000, as has the percentage of immunised children.
Bill Gates said 300 million Africans who depend on maize are going to get new varieties that are drought-resistant and will boost productivity.