Solve {l}{x+y=240}{156.3x+168.3y+161*120=161.8*360}

$$\left\{ \begin{array} { l } { x + y = 240 } \\ { 156.3 x + 168.3 y + 161 \times 120 = 161.8 \times 360 } \end{array} \right.$$

Solve for x, y

$$x=122$$

$$y=118$$

Steps Using Substitution

To solve a pair of equations using substitution, first solve one of the equations for one of the variables. Then substitute the result for that variable in the other equation.

$$x+y=240,156.3x+168.3y+19320=58248$$

Choose one of the equations and solve it for x by isolating x on the left hand side of the equal sign.

$$x+y=240$$

Subtract y from both sides of the equation.

$$x=-y+240$$

Substitute -y+240 for x in the other equation, 156.3x+168.3y+19320=58248.

$$156.3\left(-y+240\right)+168.3y+19320=58248$$

Multiply 156.3 times -y+240.

$$-156.3y+37512+168.3y+19320=58248$$

Add -\frac{1563y}{10} to \frac{1683y}{10}.

$$12y+37512+19320=58248$$

Add 37512 to 19320.

$$12y+56832=58248$$

Subtract 56832 from both sides of the equation.

$$12y=1416$$

Divide both sides by 12.

$$y=118$$

Substitute 118 for y in x=-y+240. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=-118+240$$

Add 240 to -118.

$$x=122$$

The system is now solved.

$$x=122,y=118$$

Steps Using Matrices

Put the equations in standard form and then use matrices to solve the system of equations.

$$x+y=240,156.3x+168.3y+19320=58248$$

Write the equations in matrix form.

$$\left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}240\\38928\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right).

$$inverse(\left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right))\left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right))\left(\begin{matrix}240\\38928\end{matrix}\right)$$

The product of a matrix and its inverse is the identity matrix.

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right))\left(\begin{matrix}240\\38928\end{matrix}\right)$$

Multiply the matrices on the left hand side of the equal sign.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}1&1\\156.3&168.3\end{matrix}\right))\left(\begin{matrix}240\\38928\end{matrix}\right)$$

For the 2\times 2 matrix \left(\begin{matrix}a&b\\c&d\end{matrix}\right), the inverse matrix is \left(\begin{matrix}\frac{d}{ad-bc}&\frac{-b}{ad-bc}\\\frac{-c}{ad-bc}&\frac{a}{ad-bc}\end{matrix}\right), so the matrix equation can be rewritten as a matrix multiplication problem.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{168.3}{168.3-156.3}&-\frac{1}{168.3-156.3}\\-\frac{156.3}{168.3-156.3}&\frac{1}{168.3-156.3}\end{matrix}\right)\left(\begin{matrix}240\\38928\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{561}{40}&-\frac{1}{12}\\-\frac{521}{40}&\frac{1}{12}\end{matrix}\right)\left(\begin{matrix}240\\38928\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{561}{40}\times 240-\frac{1}{12}\times 38928\\-\frac{521}{40}\times 240+\frac{1}{12}\times 38928\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}122\\118\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=122,y=118$$

Steps Using Elimination

In order to solve by elimination, coefficients of one of the variables must be the same in both equations so that the variable will cancel out when one equation is subtracted from the other.

$$x+y=240,156.3x+168.3y+19320=58248$$

To make x and \frac{1563x}{10} equal, multiply all terms on each side of the first equation by 156.3 and all terms on each side of the second by 1.

$$156.3x+156.3y=156.3\times 240,156.3x+168.3y+19320=58248$$

Simplify.

$$156.3x+156.3y=37512,156.3x+168.3y+19320=58248$$

Subtract 156.3x+168.3y+19320=58248 from 156.3x+156.3y=37512 by subtracting like terms on each side of the equal sign.

$$156.3x-156.3x+156.3y-168.3y-19320=37512-58248$$

Add \frac{1563x}{10} to -\frac{1563x}{10}. Terms \frac{1563x}{10} and -\frac{1563x}{10} cancel out, leaving an equation with only one variable that can be solved.

$$156.3y-168.3y-19320=37512-58248$$

Add \frac{1563y}{10} to -\frac{1683y}{10}.

$$-12y-19320=37512-58248$$

Add 37512 to -58248.

$$-12y-19320=-20736$$

Add 19320 to both sides of the equation.

$$-12y=-1416$$

Divide both sides by -12.

$$y=118$$

Substitute 118 for y in 156.3x+168.3y+19320=58248. Because the resulting equation contains only one variable, you can solve for x directly.

$$156.3x+168.3\times 118+19320=58248$$

Multiply 168.3 times 118.

$$156.3x+19859.4+19320=58248$$

Add 19859.4 to 19320.

$$156.3x+39179.4=58248$$

Subtract 39179.4 from both sides of the equation.

$$156.3x=19068.6$$

Divide both sides of the equation by 156.3, which is the same as multiplying both sides by the reciprocal of the fraction.

$$x=122$$

The system is now solved.

$$x=122,y=118$$