A software engineer at Neverware, a company that replaces computers

A software engineer at Neverware, a company that replaces computers in schools with terminals connected to a server, is testing a new server to see if mean download times are decreased with the new server. When he compares a random sample of 20 times to the previous standard he gets a t-statistic of – 15. ,a) Explain what the t- statistic means in this context. ,b) Look up the 0.001 lower critical value for a t-statistic with 19 df and state your conclusion about the test. ,c) Why did you probably not need to look up the critical value in b) to reach your conclusion?