solve for x and y...I tried solving by elimination and substitution by taking LCM etc but the answer I obtain doesn't match with the answer key.
What about the below question ? Are you getting 15?
Fatherís age is three times the sum of ages of his two children. After 5 years his age will be twice the sum of age of his two children. Find the age of father.
IF fathers age is really 15 then the sum of ages of children must be 5. 5 years from now, his age will be 20 and both the children's age will advance by 5. Thus totally the sum of their ages will be 15 after 5 years. BUT two times 15 is not 20!
So your answer is wrong.
Let the fathers age be '3x', then the sum of children's age is x. 5 years from now fathers age will be 3x+5, but the sum of children's age will be x+10. Remember that there are two people and both of them advance by 5 years.
Now by given data:
So fathers age is 3x = 45 years.
Now backtrack this and see if its right!