Question 323929

Robert<font color = "red">, who is now R years old,</font> is 4/5 as old as Joel<font color = "red">, who is now J years old</font>. 
`
So {{{R}}}{{{""=""}}}{{{4/5}}}{{{J}}}
`
Four years ago <font color = "red">when Robert was R-4</font>, he was 3/4 as old as Joel <font color = "red">was four years ago, which was J-4</font>.
`
So {{{R-4}}}{{{""=""}}}{{{3/4}}}{{{(J-4)}}}
`
Therefore we have the system of equations:
`
{{{system(R=(4/5)J, R-4=(3/4)(J-4))}}}
`
Clear them of fractions:
`
{{{system(5R=4J, 4(R-4)=3(J-4))}}}
`
Can you solve that system?  If not post again asking how.
`
R=16, J=20
`
  Robert<font color = "red">, who is 16,</font> is 4/5 as old as Joel <font color = "red">, who is 20, and indeed 4/5 of 20 = (4/5)x(20)=16</font>. Four years ago, <font color = "red">he was 16 and Joel was 12, that is,</font> 3/4 as old as Joel<font color = "red">, and indeed 3/4 of 16 is (3/4)x(16)=12</font>. 

Edwin</pre>