If one number is thrice the other and their sum is $16$, find the numbers If one number is thrice the other and their sum is $16$, find the numbers.
I tried, 
Let the first number be $x$ and the second number be $y$
Acc. to question  
$$
\begin{align}
x&=3y &\iff x-3y=0 &&(1)\\
x&=16-3y&&&(2)
\end{align}
$$

Let the first number be $x$
And second which is thrice be $3y$
Acc to ques.. 
$x=3y\ldots \textrm{equation 1}$
$x+y=16\ldots\textrm{equation 2}$
By Elimination method 
       x-3y  =    0
     -(x+ y) =  -16
     ______________
       0- 4y = - 16

Dividing the equation by $(-4)$. The result is $y=4$
Put $y=4$ into the first equation :$x=3\cdot 4\Rightarrow x=12$
I hope this will help you.. Thank you!
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