Solution:Â Â
Standard Error Formula:Â Â
 SExĚ„ = S / UNDERROOT N Â
 where,Â
 SExĚ„ = Standard Error of the Mean Â
 s = Standard Deviation of the Mean Â
 n = Number of Observations of the Sample Â
 SExĚ„ = 51.60/ âš21 = 11.26004314Â
 So, standard error = 11.26004314