Question 463435
1st student's age = a
2nd student's age = b
3rd student's age = c


a + b + c = 60
a + b - c = 12
c = 5 + a


a + b + c = 60
a + b - c = 12
--------------- (-)
2c = 48
c = 48/2 = 24


c = 5 + a
24 = 5 + a
a = 24 - 5 = 19


a + b + c = 60
19 + b + 24 = 60
43 + b = 60
b = 60 - 43 = 17


so,
1st student's age = 19
2nd student's age = 17
3rd student's age = 24