Apple tumbled after it disappointed Wall Street with a forecast that indicated growth would stay subdued in the quarter where the holiday season usually drives its most robust sales. The world’s most valuable firm was set to lose more than $80 billion in market value, based on its premarket share price of $172. Its shares have rallied nearly 40% this year. The tech giant reported quarterly earnings on Thursday that topped estimates. Still, its forecast sent shares down, stoking concerns
