The biggest school admissions scandal ever prosecuted began with a tip from an executive investigators were targeting in an unrelated securities fraud probe, it was revealed today. The unnamed businessman told Boston authorities chasing down the market manipulation scheme that Rudy Meredith, the women’s soccer coach at Yale University, said he would designated the executive’s daughter as a recruit in exchange for cash, the official said. The official was not authorized to discuss the case and spoke on the condition of anonymity.