Q.a. doubt

Standard error = σ/√n  the sampling mean for large values of n follows a normal distribution so for 0.95 certainty the population mean should be inside sample mean +/-  1.96*standard error

so 1.96*SE  = σ/10 implies 1.96/ √n = 0.1  implies √n = 19.6 implies n = 19.6² = 384.16 = 384 so answer is b

how it is came from s.e -1.96

look up z tables

i cant understand.

for normal distribution there are z tables which tell you how much percentage of values fall in between x standard deviations from mean. for 95% of values to fall between mean and standard deviation, the length of the interval will be mean +/- 1.96 standard deviations.

thnks a lot.