A frequency table has been used to report the length of life of a component. The table has eight intervals and has been used to calculate the sample mean and sample standard deviation. It has been decided to test at the 1 per cent significance level whether the length of life follows a normal distribution. A chi-squared test statistic of 13.246 was calculated by comparing the observed and expected frequencies (with all expected frequencies above five). You would compare the chi-squared value with a critical value of:
a. 11.1 and not reject the null hypothesis
b. 11.1 and reject the null hypothesis
c. 15.1 and not reject the null hypothesis
d. 15.1 and reject the null hypothesis