SOLUTION: Robert is 4/5 as old as Joel. Four years ago, he was 3/4 as old as Joel, how old are they now?

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Question 323929: Robert is 4/5 as old as Joel. Four years ago, he was 3/4 as old as Joel, how old are they now?
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!

Robert, who is now R years old, is 4/5 as old as Joel, who is now J years old.
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So R%22%22=%22%224%2F5J
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Four years ago when Robert was R-4, he was 3/4 as old as Joel was four years ago, which was J-4.
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So R-4%22%22=%22%223%2F4%28J-4%29
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Therefore we have the system of equations:
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system%28R=%284%2F5%29J%2C+R-4=%283%2F4%29%28J-4%29%29
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Clear them of fractions:
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system%285R=4J%2C+4%28R-4%29=3%28J-4%29%29
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Can you solve that system? If not post again asking how.
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R=16, J=20
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Robert, who is 16, is 4/5 as old as Joel , who is 20, and indeed 4/5 of 20 = (4/5)x(20)=16. Four years ago, he was 16 and Joel was 12, that is, 3/4 as old as Joel, and indeed 3/4 of 16 is (3/4)x(16)=12.
Edwin