<PRE><B>Question 923124</B>
The average age of Kevin, Joe and Nick is 19
sum of their age :  sum  = average *no of persons
                          =19*3
                          = 57 
average age of Joe and Nick is 17
              sum of ages of joe and nick   = 2*17 = 34
so , age of Kevin  = sum of their age -sum of ages of joe and nick
                    =57-34
                   =23 years
result is 23 years</PRE>