hi
can anybody help me

a) what does standard deviation describe about a set of data?
b)Table below shows the crushing strengths of concrete samples, determine
1) Mode, mean and median and standard deviation
2) standard deviation likely for the population

261, 245, 385, 253, 298, 284, 320, 335, 297, 335
300, 314, 345, 310, 279, 298, 305, 298, 320, 300

thanks