According to a Pew Poll done in 2010, 50% of adults aged 25-29 had access only to a cell phone (no landline). Assume that you randomly sample 50 adults aged 25-29, and ask whether they have access only to a cell phone. Suppose that 30 say yes and 20 say no. Calculate the observed value of the chi-square statistic for testing the hypothesis that 50% have a cell phone only.