Airbnb says its second-quarter profit rose more than 70% from a year ago to $650 million thanks to strong bookings for summer-vacation rentals. The San Francisco company said Thursday that bookings grew 11% over the same period last year. That helped lift revenue. The second-quarter results beat Wall Street forecasts, according to a survey by FactSet. Airbnb predicts that bookings and average rates for rentals will remain strong in the July-through-September quarter, driving revenue slightly higher than analysts' expectations over the rest of the summer.