Question: In testing a trial type of battery, 20 batteries were placed on test and observed for 12 hours. In that time 11 of the batteries stopped working with their times until this occurred being recorded in hours as 3.5, 4.7, 6.5, 7.5, 8.2, 9.4, 9.8, 10.3, 10.6, 10.8, 11.5. Estimate the mean time of (continuous) operation until failure for this type of battery.