Reuters Quote: Dow, S&P 500 Lower on Mixed Earnings; Nasdaq Rises
* Amazon jumps after posting unexpected profit * Visa rises after results beat expectations * Biogen slumps after slashing forecast * Futures: Dow down 31 pts, S&P down 2 pts, Nasdaq up 3 pts (Adds details, comment, updates prices) By Tanya Agrawal July 24 (Reuters) – Wall Street was set to open slightly lower on…