import numpy as np
import scipy.stats as stats
#from scipy.stats import norm
#from scipy.stats import t

time = [66, 37, 18, 31, 85, 63, 73, 83, 65, 80]
print("Data of time variable is :", time)

df=len(time)-1

s2 = np.var(time, ddof=1)

chi_u = stats.chi2.ppf(0.975, df)
chi_l = stats.chi2.ppf(0.025, df)

print("Upper Critical Value of Chi2 w/ df=15 is :", chi_u)
print("Lower Critical Value of Chi2 w/ df=15 is :", chi_l)

LCL = (df*s2/chi_u)
UCL = (df*s2/chi_l)

print("Lower Value of 95% Confidence Interval is :", LCL)
print("Upper Value of 95% Confidence Interval is :", UCL)