Question 448793
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A first number plus twice a second number is 8. Twice the first number, plus the second number totals 25. 
Find the numbers.
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        There is very easy and effective way to solve it - practically mentally,  in the head.



<pre>
The equations are

     x + 2y =  8    (1)

    2x +  y = 25    (2)


Add the equations

    3x + 3y = 33,

hence

    x + y = 11.     (3).


Compare (1) and (3).  It should be clear from the comparison that  y = -3.


Next, compare equations (2) and (3).  It should be clear for the comparison that  x = 14.


Now check these values and makes sure that they satisfy equations.
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That's all.