Averages and measures of spread — practice question

A dentist has appointments with 10 patients one morning. The stem-and-leaf diagram gives the waiting times for 8 of them. These listed times are 1, 4, 10, 12, 19, 21, 25, 25 minutes. Key: 1|0 represents 10 minutes. The waiting times for the other two patients, P and Q, are not included on the stem-and-leaf diagram. The mean waiting time for all 10 patients that morning is 16 minutes. The range of the waiting times is 26 minutes. Patient P waits for longer than patient Q.