ginarusso470 ginarusso470

23-02-2016
Mathematics

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A first number plus twice a second number is 9. Twice the first number plus the second totals 21. Find the numbers

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crisforp crisforp

23-02-2016

Let x and y be the numbers;
We have x + 2y = 9 and 2x + y = 21;
Then, x = 9 - 2y;
Finally, 2(9-2y) + y = 21 ;
18 - 4y + y = 21;
18 - 3y = 21;
-3y = 3;
y = - 1;
x = 9 - 2× (-1);
x = 9 + 2 ;
x = 11;

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