Salman Khan was in his twenties and working as a hedge fund analyst in Boston when his 12-year-old cousin from New Orleans asked him for some help with maths. He started tutoring Nadia over the telephone and she went from the remedial class to being the top maths student in her school.
Soon Khan was giving remote lessons in algebra and calculus to 15 cousins in Louisiana. He set up a website, wrote software that generated practice questions and recorded videos to put on YouTube. People outside the family began to notice them and before long tens of thousands were watching his online tutorials every month.
Then Bill Gates told a conference that he had been using Khan’s videos to teach his children maths and
