While on his death-bed in 1920, Ramanujan wrote a letter to his mentor, British mathematician GH Hardy, outlining several new mathematical functions never before heard of, along with a hunch about how they worked, the Daily Mail reported. Now, researchers say they have proved Ramanujan was right, and that the formula could explain the behaviour of black holes. "We've solved the problems from his last mysterious letters," Ken Ono, a mathematician from Emory University in Georgia, US, was quoted as saying. "For people who work in this area of math, the problem has been open for 90 years," he said. Ono said Ramanujan, a self-taught mathematician born in a village in southern India, spent so much time thinking about math that he flunked out of college in India twice. Ramanujan's letter to Hardy described several new functions that behaved differently from known theta functions, or modular forms, and yet closely mimicked them. Ramanujan, a devout Hindu, thought these patterns were revealed to him by the goddess Namagiri. However, no one at the time understood what he was talking about.