'What is an app?': Warren Buffett enlisted Apple CEO Tim Cook to teach him how to use his new iPhone

• Warren Buffett, who only recently switched from a $20 flip phone to an iPhone, received personal instruction from Apple's CEO on how to use the device.
• "I went out to California, and Tim Cook very patiently spent hours trying to move me up to the level of the average two-year-old," the 89-year-old investor told Yahoo Finance. "Didn't quite make it."
• Buffett visited Cook to film a video in which he appears to develop an app, but was left with a burning question after they finished shooting.
• "As I walked out, I turned to Tim, and I said, 'By the way, what is an app?'"
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Warren Buffett received personal instruction from Apple CEO Tim Cook on how to use an iPhone, he told Yahoo Finance in a March 10 interview that was released on Thursday.

"I went out to California, and Tim Cook very patiently spent hours trying to move me up to the level of the average two-year-old," the 89-year-old investor and Berkshire Hathaway boss said. "Didn't quite make it."

Buffett, who only recently switched his $20 flip phone for the iPhone 11, visited Cook to film a video in which he appears to develop an app. On his way out the door, he asked Cook for a final pointer on the technology.

"As I walked out, I turned to Tim, and I said, 'By the way, what is an app?'"

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Buffett resisted the Apple chief's efforts to upgrade him to an iPhone for several years.

"Tim Cook sent me a Christmas card again this year saying he's going to sell me an iPhone this year," Buffett told CNBC in January 2018.

Cook also reassured Buffett of a smooth transition to the smartphone era.

"I told him I'll personally come out to Omaha and do tech support for him," he said on Bloomberg TV in June 2018.

Buffett praised Cook and Apple, Berkshire's biggest holding, during the Yahoo Finance interview.

"It's an incredible business run by a fellow who is one of of the great managers of all time," he said. "He was underrated for a while but now he's being seen for what he really is."