tablet computer manufacturer claims that its batteries last an average of 11.5 hours when playing videos. The quality-control department randomly selects 20 tablets from each day's production and tests the fully charged batteries by playing a video repeatedly until the battery dies. The quality-control department will discard the batteries from that day's production run if they find convincing evidence that the mean battery life is less than 11.5 hours. Given are a dotplot and summary statistics of the data from one day:
