The rule of thumb for this construction is stated succinctly by Bernstein 1977:My inclination would still be to treat Rosie's phrase as contained within standard English usage, but GL is certainly not incorrect; to the contrary, the usage he favours is apparently more standard.In general, a number takes a plural verb and the number a singular.Evidence in the Merriam-Webster files shows that the rule of thumb is generally observed. Even when the sentence begins with there, a number of commands the plural verb. {example] An adjective like increasing or growing tends to emphasise the word number in its singularity, and results in rather more mixed usage. [examples] But even in these constructions, the plural verb is the more common.