The city can start hiring new teachers and administrators to fill positions at 24 schools that will be closed and reopened by September, under a deal reached with the teachers' and principals' unions and announced late Friday. An arbitrator, meanwhile, will work quickly to decide whether the city's shuffling of staff violates the unions' contract. If the city loses the arbitration, its new hiring can be reversed.

Facebook’s $16 billion offering was the biggest I.P.O. that Nasdaq had ever listed. Now there are growing questions over how it was handled.