Solve the system by using either the substitution method or the elimination-by-addition method, whichever seems more appropriate. $\left( \begin{array} { lll }
y &=& 3 x \
0.31 x &+& 0.09 y &= &232
\end{array} \right)$
A) (600, 1,800)
B) (400, 1,200)
C) dependent
D) inconsistent

Question

Solve the system by using either the substitution method or the elimination-by-addition method, whichever seems more appropriate. $\left( \begin{array} { lll } 
y &=& 3 x \
0.31 x &+& 0.09 y &= &232
\end{array} \right)$
A) (600, 1,800)
B) (400, 1,200)
C) dependent
D) inconsistent

Quizplus · Accepted Answer

Substitution method is appropriate here as we can solve for y in the first equation and substitute it in the second equation. 
y = 3x 
0.31x + 0.09y = 232 
0.31x + 0.09 (3x) = 232  [substituting y = 3x]
0.58x = 232 
x = 400 
Substituting x = 400 in the first equation, 
y = 3x = 1,200 
Therefore, the solution is (400, 1,200) which is option B.

Solve the System by Using Either the Substitution Method or the Elimination-By-Addition