Question

The ratio of ages (in years) of three children is 2:4:5. The sum of their ages is 33. What is the ages of each child ?

Answer 1

2+4+5 is 11 and 33/11 is 3 so for every 1 is 3 years,
 the first is 2 so is 2x3=6
the second is 4 so is 4x3=12
the third is 5 so is 5x3=15

Answer 2

You could also write it as:
1st child's age:= 2x
2nd child:= 4x
3rd child:= 5x
2x+4x+5x=33
11x=33
x=3
Then
1st child's age:= 2x= 6
2nd child:= 4x= 12
3rd child:= 5x= 15
To check if it's correct you need to sum up: 6+12+15=33