Find the significance levels that reject a claim

At an early stage in analysing the marks scored by a large number of candidates in an examination paper, the Examining Board takes a random sample of 250 candidates and finds that their marks satisfy $\sum x=11872$ and $\sum x^2=646193$. Using these figures, the null hypothesis $\mu=49.5$ is tested against the alternative $\mu<49.5$ at the $\alpha\%$ level of significance. Determine $\alpha$ for which the null hypothesis is rejected in favour of the alternative hypothesis.