SOLUTION: A man is three times as old as his son, and his daughter is four years younger than his son. If the combined ages of all three is 81 years, find the present age of the father.

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Question 313306: A man is three times as old as his son, and his daughter is four years younger than his son. If the combined ages of all three is 81 years, find the present age of the father.
Ps: Thank you, please demonstrate the work progress so I will know how to do the question next time please and thank you :D
Answer by ntnk(54) About Me  (Show Source):
You can put this solution on YOUR website!
So for these you have to turn the statements in the word problem into equations.
A man is three times as old as his son: +M+=+3+%2A+S+
his daughter is four years younger than his son: +D+=+S+-+4+
combined ages of all three is 81 years: +M+%2B+D+%2B+S+=+81+
Now you can just substitute: +%283%2AS%29+%2B+%28S-4%29+%2BS+=+81+
+5%2AS+-+4+=+81+
Add 4 to both sides to get: 5%2AS+=+85+
Divide by 5 on both sides to get: +S+=+17+
Now check: +M+=+3+%2A+S+=+3+%2A+17+=+51+ and +D+=+S+-+4+=+17+-+4+=+13+,
so +M+%2B+D+%2B+S+=+51+%2B+13+%2B+17+=+81+, so we do indeed get the combined age as 81, which means our son's age of 17 is correct!
I hope that helps!
-ntnk