A) mean = average. Find the total of the ages and dive by number of people:
19x 2 = 38
20x3= 60
21x1= 21
22x4 = 88
23x1=23
38 +60 +21+88+23= 230
230/ 11= 20.9
Mean = 20.9
B ) 1 more person makes the total 12 people. The mean becomes 22, so total of the ages would be 12x22= 264
Subtract the two totals 264 - 230 = 34
The person would be 34