Answer:
Mean = 272.3
sd = 37.7
Explanation:
Mean = sum/n
(221+248+251+255+259+263+264+272+291+297+374) ÷ 11
= 2995/11
= 272.2727273
Variance = (sum of x²)/n - mean²
[(221²+248²+251²+255²+259²+263²+264²+272²+291²+297²+374²)/11] - (2740/11)²
= (831067/11) - (2995/11)²
= 1419.107438
sd² = variance
sd = sqrt(1419.107438)
sd = 37.67104243