Question 1131613
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Since the solution by @addingup is &nbsp;<U>ABSOLUTELY WRONG</U>, &nbsp;I came to bring the correct solution.



<pre>
A = S-10      (1)
S+10 = 3A     (2)


Substitute expression  A = S-10  from eq(1) into eq(2), replacing A in equation (2).


S + 10 = 3*(S-10)

S + 10 = 3S - 30

10 + 30 = 3S - S

2S = 40   ====>  S = 40/2 = 20.


<U>ANSWER</U>.  Scott is 20 years now.  Allen is 20-10 = 10 years now.


<U>Check</U>.   Eq(1):  A = S-10:   10 = 20-10      ! Correct !

         Eq(2):  S+10 = 3A:  20+10 = 3*10    ! Correct !
</pre>

Solved and checked.