Distinguish unbiased variance, estimated SD and significance

A Mathematics test is administered to a large group. For 200 recorded scores, $\sum(x+10)=12290$ and $\sum(x+10)^2=811212$.

(i) Find unbiased estimates of the population mean and standard deviation.

(ii) Test at 5% whether the population mean score exceeds 50. State, with a reason, whether assumptions about the population distribution are needed.

The alternative hypothesis is accepted at $\alpha\%$ significance.

(iii) Find an inequality satisfied by $\alpha$.

(iv) Explain “$\alpha\%$ level of significance” in this context.