Bill and Melinda Gates pen love letter to Warren Buffett

Ten years ago, billionaire investor Warren Buffett generously donated $30 billion to the Bill & Melinda Gates foundation, marking "the biggest single gift anyone ever gave anybody for anything."

Now a decade later, on Valentine's Day of all holidays, Bill and Melinda Gates have dedicated their annual letter to their friend, Buffett, whose donation help propel the foundation to "success" in some of its key charitable initiatives.

"Warren, your gift doubled the foundation's resources. It's allowed us to expand our work in US education, support smallholder farmers, and create financial services for the poor."

The letter was prompted by a request Buffett made in December for the pair to explain the success and motivation of the Bill & Melinda Gates Foundation.

In return, the Gates on Tuesday showed Buffett -- and the world -- Buffett's "return on investment."

But it's not all numbers and charts. In addition to stunning facts and figures, the piece also features hand-written anecdotes, like "Who brings McDonald's coupons on vacation? You do, that's who!" when illustrating one of Buffett's "deepest values" -- using resources wisely and never wasting money when it can be avoided.

RELATED: Bill Gates through the years

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Bill Gates through the years
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Bill Gates through the years

Microsoft Co-founder Bill Gates

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Microsoft co-founder Bill Gates and his girlfriend Jill Bonnett. 

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Microsoft Co-founder Bill Gates Holding a CD-ROM

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Microsoft CEO Bill Gates

(Doug Wilson/CORBIS/Corbis via Getty Images)

Microsoft president Bill Gates demonstrates Microsoft's Windows 95 program from his automobile prior to a press conference in Paris 04 September. Gates was also to meet 500 top computer executives as part of his campaign to launch the company's new software.

(Michel GANGN/AFP/Getty Images)

(Photo by Lynn Goldsmith/Corbis/VCG via Getty Images)

Microsoft Chairman Bill Gates visits an expo previewing Windows XP October 24, 2001 in New York City. The Windows XP operating system goes on sale worldwide October 25.

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Microsoft chairman Bill Gates testifies at Senate Judiciary Committee hearing into whether the Microsoft computer empire is a monopoly that buries the competition.

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Bill Gates holds baby girl Cecil Massango during his visit to the Manhica Health Research Centre in Mozambique September 21, 2003. The Bill and Melinda Gates Foundation announced three grants totalling 168 million dollars to fight malaria, a disease that due to increased drug resistance, is on the rise in Africa for the first time in 20 years, killing more than one million people annually.

(REUTERS/Juda Ngwenya)

Bill Gates, Chairman and Chief Software Architect at Microsoft, talks to reporters as Microsoft announced the general availability of the new Microsoft Office System, October 21, 2003 in New York City. "The new Office System is a major leap forward for information workers," said Gates, "It makes information work more productive and more profitable by offering innovative new ways to communicate, to find and share information, and to manage complex projects."

(REUTERS/Jeff Christensen)

Former US President Bill Clinton, left, speaks as Bill Gates, chairman, Microsoft Corp. looks on during a session on the G-8 and Africa during the World Economic Forum in Davos, Switzerland on January 27, 2005.

(Photo by Adam Berry/Bloomberg via Getty Images)

Microsoft Chairman Bill Gates delivers the keynote speech at the fourteenth RSA conference at the Moscone Center February 15, 2005 in San Francisco, California. Gates spoke about internet security and new technology that can recognize spyware that might infiltrate a computer.

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Swatch CEO Nick Hayek and Microsoft CEO Bill Gates attend a press conference for the launch of the new Swatch line 'Paparazzi' by Swatch and Microsoft on October 20, 2004 in New York City.

(Photo by Peter Kramer/Getty Images)

Microsoft chairman and chief software architect Bill Gates smiles during a news conference in Madrid November 19, 2004. Gates signed a technology agreement with the Madrid regional government.

(REUTERS/Andrea Comas)

Microsoft Corp. Chairman Bill Gates (L) shakes hands with singer Justin Timberlake during his keynote address at the Consumer Electronics Show in Las Vegas January 4, 2006. Gates took the wraps off its next-generation operating system known as Windows Vista on Wednesday, displaying features aimed at positioning the software giant as the entertainment hub for a future of digitally connected homes.

(REUTERS/Rick Wilking)

Bill Gates attends the Director's Brunch during the 2010 Sundance Film Festival a Sundance Resort on January 23, 2010 in Park City, Utah.

(Photo by Fred Hayes/Getty Images)

Microsoft Corp co-founder Bill Gates (L) interacts with a villager in Aulali village, in Khagaria district of the eastern Indian state of Bihar, May 12, 2010. Gates is on a day-long visit to the state.

(REUTERS/Stringer)

Bill Gates, the coo-founder and former chief executive of Microsoft, celebrates his 60th birthday. He was born on October 28, 1955. --- In photo: Bill Gates during a press conference in Berlin, on January 29, 2013. 

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Microsoft founder Bill Gates makes a speech after receiving the Millennium Bambi during the Bambi 2013 media awards ceremony in Berlin November 14, 2013. The annual Bambi awards honours celebrities from the world of entertainment, literature, sports and politics.

(REUTERS/Tobias Schwarz)

Billionaire philanthropist and Microsoft's co-founder Bill Gates delivers the 14th Nelson Mandela Annual Lecture on the eve of Mandela Day under the theme "Living Together" in his lecture at the University of Pretoria, South Africa, July 17, 2016.

(REUTERS/Siphiwe Sibeko)

Bill Gates, the co-Founder of the Microsoft company and co-Founder of the Bill and Melinda Gates Foundation makes a statement after his meeting with French President Francois Hollande at the Elysee Presidential Palace on June 27, 2016 in Paris, France. Bill Gates mentioned in a short statement after his meeting with French President Francois Hollande that France was a great asset in the fight against AIDS.

(Photo by Chesnot/Getty Images)

Billionaire Bill Gates, co-founder of the Bill & Melinda Gates Foundation, center, arrives at Trump Tower in New York, U.S., on Tuesday, Dec. 13, 2016. Exxon Mobil Corp. Chief Executive Officer Rex Tillerson will be nominated as President-elect Donald Trump's secretary of state, setting up a potential confirmation battle with U.S. lawmakers who have questioned the oilman's relationship with Russian President Vladimir Putin.

(John Taggart/Bloomberg via Getty Images)

U.S. President Barack Obama (R) presents the Presidential Medal of Freedom to Melinda and Bill Gates during a ceremony in the White House East Room in Washington, U.S., November 22, 2016.

(REUTERS/Carlos Barria)

Chairman and Chief Software Architect for Microsoft Corporation Bill Gates delivers the opening keynote address for the 2006 International Consumer Electronics Show (CES) at the Las Vegas Hilton. Gates provided an overview of the latest devices and outlined the company's vision for the future by previewing upcoming products like Windows Vista.

(Photo by Chris Farina/Corbis via Getty Images)

Microsoft Chairman Bill Gates (R) talks with Sen. Bernard Sanders (I-VT) (L) after testifying before the Senate Health, Education, Labor and Pensions Committee March 7, 2007 in Washington, DC. Gates called for more government spending in education and training, especially in high school math and science. He called high schools in their current form a barrier to success in the digital age.

(Photo by Win McNamee/Getty Images)

United States President George W. Bush, First Lady Laura Bush and daughter Barbara Bush and former Microsoft Chairman Bill Gates attend the National Aquatics Center on Day 3 of the Beijing 2008 Olympic Games on August 11, 2008 in Beijing, China.

(Photo by Shaun Botterill/Getty Images)

Warren Buffett, Bill Gates and Ludacris watch the USA Basketball Men's Senior National Team play against the Canadian National Team during the State Farm USA Basketball Challenge on July 25, 2008 at the Thomas and Mack Center in Las Vegas, Nevada.

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Bill Gates, Chairman of Microsoft speaks in Hong Kong on August 12, 2008. Gates was giving a speech at Microsoft Research Asia 10th Anniversary Innovation Forum.

(MIKE CLARKE/AFP/Getty Images)

Bill Gates and director Pablo Larcuen attend the Director's Brunch during the 2010 Sundance Film Festival a Sundance Resort on January 23, 2010 in Park City, Utah.

(Photo by Fred Hayes/Getty Images)

Bill Gates tours and interacts with students in the engineering lab at Science Leadership Academy (SLA) prior to the 2010 Franklin Institute Awards held at The Franklin Institute on April 29, 2010 in Philadelphia City.

(Photo by Gilbert Carrasquillo/Getty Images)

Microsoft founder and philanthropist Bill Gates (R) shakes hands with France Finance and Economy Minister Christine Lagarde as he leaves the Elysee Palalce in Paris on April 4, 2011, after a meeting with French President Nicolas Sarkozy. Gates is in visit to France for his foundation's Living Proof Project to highlight successes of US-funded global health initiatives.

(LIONEL BONAVENTURE/AFP/Getty Images)

Microsoft founder and philanthropist Bill Gates poses on April 4, 2011 in Paris, as part of his campaign 'Living Proof' for the Bill & Melinda Gates foundation.

(MIGUEL MEDINA/AFP/Getty Images)

Bill Gates founder of Microsoft and Bono, singer of U2 meet with President Francois Hollande of France at the Elys Palace to discuss humanitarian projects to fight poverty around the world and support economic development in poor countries.

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French President Francois Hollande (R) welcomes Bill Gates, the co-Founder of the Microsoft company and co-Founder of the Bill and Melinda Gates Fondation, at the Elysee Presidential Palace, in Paris, France, on April 1, 2014.

(ERIC FEFERBERG/AFP/Getty Images)

Bill Gates, founder of Microsoft and co-chairman of the Bill and Melinda Gates Foundation, addresses the National Board for Professional Teaching Standards' inaugural Teaching and Learning Conference in Washington,DC on March 14, 2014.

(NICHOLAS KAMM/AFP/Getty Images)

THE TONIGHT SHOW STARRING JIMMY FALLON

Episode 0199

Pictured: (l-r) Bill Gates during an interview with host Jimmy Fallon on January 21, 2015 

(Photo by: Douglas Gorenstein/NBC/NBCU Photo Bank via Getty Images)

Lin Manuel Miranda and Bill Gates pose backstage at the hit musical 'Hamilton' on Broadway at The Richard Rogers Theater on October 11, 2015 in New York City.

(Photo by Bruce Glikas/FilmMagic)

Bill Gates, the co-Founder of the Microsoft company and co-Founder of the Bill and Melinda Gates Foundation visits and speaks at the Solidays festival on June 26, 2015 in Paris, France. Bill Gates visited the 17th edition of the Solidays music festival, dedicated to the fight against AIDS.

(Photo by Francois Pauletto/Corbis via Getty Images)

Bill Gates attends the official opening of the Barberini Museum on January 20, 2017 in Potsdam, Germany. The Barberini, patronized by billionaire Hasso Plattner, features works by Monet, Renoir and Caillebotte among others.

(Photo by Axel Schmidt - Pool/Getty Images)

Bill Gates, billionaire and co-chair of the Bill and Melinda Gates Foundation, gestures as he speaks during a Bloomberg Television interview during the World Economic Forum (WEF) in Davos, Switzerland, on Wednesday, Jan. 18, 2017. World leaders, influential executives, bankers and policy makers attend the 47th annual meeting of the World Economic Forum in Davos from Jan. 17 - 20.

(Simon Dawson/Bloomberg via Getty Images)

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While "philanthropy isn't like business," the Gates wrote, and there aren't sales and profits to share, there are numbers that measure the foundation's progress. Here are just a handful of the many highlights detailed in the full letter:

  • 122 million children's lives saved since 1990 - "Saving children's lives is the goal that launched our global work. It's an end in itself. But then we learned it has all these other benefits as well. If parents believe their children will survive—and if they have the power to time and space their pregnancies—they choose to have fewer children," Melinda wrote.
  • 86 percent of children around the world are vaccinated, the highest in history - "And for every dollar spent on childhood immunizations, you get $44 in economic benefits. That includes saving the money that families lose when a child is sick and a parent can't work," Bill wrote.
  • 300 million women in the developing world who use modern contraceptives - "Contraceptives are also one of the greatest antipoverty innovations in history. When women are able to time and space their pregnancies, they are more likely to advance their education and earn an income—and they're more likely to have healthy children," Melinda wrote.

The Gates also pinpointed some challenges in their work:

  • 1 million babies die on the day they're born - "It's not enough to know that a newborn died from asphyxia or sepsis or prematurity; we need to find out what causes these conditions, so we can find the tools to prevent them. This is the most exciting, high-stakes work we fund, Warren: solving mysteries to save lives," Bill wrote.
  • 45 percent of child deaths are due to malnutrition - "Nutrition is the biggest missed opportunity in global health. It could unleash waves of human potential—yet only 1 percent of foreign aid goes to basic nutrition ... That's why we're funding more research in this area and urging governments to do the same. Big discoveries in nutrition are ahead of us. When the researchers find them, the rise in children who achieve their potential will change the world."
  • Poverty is sexiest - "The poorer the society, the less power women have. Men decide if a woman is allowed to go outside, talk to other women, earn income. Men decide if it's acceptable to strike a woman. The male dominance in the poorest societies is mind-blowing."

Read "Dear Warren" in full here.

22 PHOTOS
What famous business leaders looked like in high school
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What famous business leaders looked like in high school
Mark Cuban

Mark Cuban may have ditched his wild 'do, but otherwise, he hasn't aged a day since he took his senior portrait in 1976!

(Classmates.com/Reuters)

Barbara Corcoran

"Shark Tank" star and real estate magnate Barbara Corcoran was a cheerleader in her heyday -- and she hasn't lost any of pep since 1969.

(Classmates.com/Getty)

Barbara Corcoran

We weren't kidding!

(Classmates.com/Getty)

Barbara Corcoran
(Classmates.com/Getty)
Warren Buffett

The business magnate was quite the dapper young man in 1947.

(Classmates.com/Getty)

Steve Wozniak

These days, the Apple co-founder opts for more casual looks than his tux in his 1968 senior portrait.

(Classmates.com/Getty)

Steve Jobs

Wozniak's business partner, Steve Jobs, rocked the man-bob in 1972.

(Classmates.com/Reuters)

Ralph Lauren

Ralph Lauren had the same penchant for plaid suits in 1957!

(Classmates.com/Reuters)

Paul Allen

Microsoft co-founder Paul Allen looked totally current with his Warby Parker-esque frames in 1969.

(Classmates.com/Getty)

Bill Gates

Plaid shirt? Check. V-neck sweater? Double-check. Bill Gates' style sure hasn't changed since the 8th grade in 1969.

(Classmates.com/AP)

Paul Allen and Bill Gates

Adorable! Allen and Gates have taken their friendship from the computer lab to the basketball court.

(Classmates.com/Getty)

Oprah Winfrey

Before Oprah was one of the biggest TV personalities and businesswomen in the world, she was voted "Most Popular" in her 1971 high school yearbook.

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Oprah Winfrey

Love those peace sign earrings!

(Classmates.com/PA)

Michael Bloomberg

No doubt 1960 Debate Club helped prepare Michael Bloomberg for a future in business and politics!

(Classmates.com/AP)

Michael Bloomberg

Just take a look at those determined eyes ...

(Classmates.com/AP)

Marissa Mayer

These days, Yahoo CEO Marissa Mayer speaks sans notecards. Here she is at her 1993 homecoming dance.

(Classmates.com/Getty)

Marissa Mayer

The only thing that's changed since this 1993 debate is Mayer's hair -- the CEO went from a wavy brunette to a straight blonde bob!

(Classmates.com/Getty)

Donald Trump

Trump's soccer days are behind him -- but his competitive spirit lives on.

(Classmates.com/Reuters)

Donald Trump

He even had a bit of the same combover in 1964!

(Classmates.com/AP)

Marcus Lemonis

"The Profit" star Marcus Lemonis, chairman and CEO of Camping World and Good Sam Enterprises, rocked a 'fro in 1988.

(Classmates.com/AP)

Abi Heller

We wonder what Classmates.com and Intelius CEO Abi Heller's former schoolmates think of his biz!

(Classmates.com)

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