John is 30 because 60 / 2 = <<60/2=30>>30
Mary is fifteen because 30 / 2 = <<30/2=15>>15
Their total age is 105 because 60 + 30 + 15 = <<60+30+15=105>>105
Their average age is 35 because 105 / 3 = <<105/3=35>>35
#### 35