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

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· *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...