Finding critical value $X^{2*}$ given significance level $\alpha$, using the table with critical $X^2$ values
Assuming a table with a row per degrees of freedom and a column per upper tail probability
Reject the null hypothesis if the observed $X^2$ falls in the highest $\alpha$ area of the $\chi^2$ distribution. In order to find the critical value $X^{2*}$ that corresponds to this upper tail area:
