Solve {l}{6.5=60x+30y}{6=40y+50x}

$$\left\{ \begin{array} { l } { 6.5 = 60 x + 30 y } \\ { 6 = 40 y + 50 x } \end{array} \right.$$

Solve for x, y

$$x=\frac{4}{45}\approx 0.088888889$$

$$y=\frac{7}{180}\approx 0.038888889$$

Steps Using Substitution

Consider the first equation. Swap sides so that all variable terms are on the left hand side.

$$60x+30y=6.5$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$40y+50x=6$$

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.

$$60x+30y=6.5,50x+40y=6$$

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

$$60x+30y=6.5$$

Subtract 30y from both sides of the equation.

$$60x=-30y+6.5$$

Divide both sides by 60.

$$x=\frac{1}{60}\left(-30y+6.5\right)$$

Multiply \frac{1}{60} times -30y+6.5.

$$x=-\frac{1}{2}y+\frac{13}{120}$$

Substitute -\frac{y}{2}+\frac{13}{120} for x in the other equation, 50x+40y=6.

$$50\left(-\frac{1}{2}y+\frac{13}{120}\right)+40y=6$$

Multiply 50 times -\frac{y}{2}+\frac{13}{120}.

$$-25y+\frac{65}{12}+40y=6$$

Add -25y to 40y.

$$15y+\frac{65}{12}=6$$

Subtract \frac{65}{12} from both sides of the equation.

$$15y=\frac{7}{12}$$

Divide both sides by 15.

$$y=\frac{7}{180}$$

Substitute \frac{7}{180} for y in x=-\frac{1}{2}y+\frac{13}{120}. Because the resulting equation contains only one variable, you can solve for x directly.

$$x=-\frac{1}{2}\times \frac{7}{180}+\frac{13}{120}$$

Multiply -\frac{1}{2} times \frac{7}{180} by multiplying numerator times numerator and denominator times denominator. Then reduce the fraction to lowest terms if possible.

$$x=-\frac{7}{360}+\frac{13}{120}$$

Add \frac{13}{120} to -\frac{7}{360} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x=\frac{4}{45}$$

The system is now solved.

$$x=\frac{4}{45},y=\frac{7}{180}$$

Steps Using Matrices

Consider the first equation. Swap sides so that all variable terms are on the left hand side.

$$60x+30y=6.5$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$40y+50x=6$$

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

$$60x+30y=6.5,50x+40y=6$$

Write the equations in matrix form.

$$\left(\begin{matrix}60&30\\50&40\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}6.5\\6\end{matrix}\right)$$

Left multiply the equation by the inverse matrix of \left(\begin{matrix}60&30\\50&40\end{matrix}\right).

$$inverse(\left(\begin{matrix}60&30\\50&40\end{matrix}\right))\left(\begin{matrix}60&30\\50&40\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}60&30\\50&40\end{matrix}\right))\left(\begin{matrix}6.5\\6\end{matrix}\right)$$

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

$$\left(\begin{matrix}1&0\\0&1\end{matrix}\right)\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}60&30\\50&40\end{matrix}\right))\left(\begin{matrix}6.5\\6\end{matrix}\right)$$

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

$$\left(\begin{matrix}x\\y\end{matrix}\right)=inverse(\left(\begin{matrix}60&30\\50&40\end{matrix}\right))\left(\begin{matrix}6.5\\6\end{matrix}\right)$$

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.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{40}{60\times 40-30\times 50}&-\frac{30}{60\times 40-30\times 50}\\-\frac{50}{60\times 40-30\times 50}&\frac{60}{60\times 40-30\times 50}\end{matrix}\right)\left(\begin{matrix}6.5\\6\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{2}{45}&-\frac{1}{30}\\-\frac{1}{18}&\frac{1}{15}\end{matrix}\right)\left(\begin{matrix}6.5\\6\end{matrix}\right)$$

Multiply the matrices.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{2}{45}\times 6.5-\frac{1}{30}\times 6\\-\frac{1}{18}\times 6.5+\frac{1}{15}\times 6\end{matrix}\right)$$

Do the arithmetic.

$$\left(\begin{matrix}x\\y\end{matrix}\right)=\left(\begin{matrix}\frac{4}{45}\\\frac{7}{180}\end{matrix}\right)$$

Extract the matrix elements x and y.

$$x=\frac{4}{45},y=\frac{7}{180}$$

Steps Using Elimination

Consider the first equation. Swap sides so that all variable terms are on the left hand side.

$$60x+30y=6.5$$

Consider the second equation. Swap sides so that all variable terms are on the left hand side.

$$40y+50x=6$$

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.

$$60x+30y=6.5,50x+40y=6$$

To make 60x and 50x equal, multiply all terms on each side of the first equation by 50 and all terms on each side of the second by 60.

$$50\times 60x+50\times 30y=50\times 6.5,60\times 50x+60\times 40y=60\times 6$$

Simplify.

$$3000x+1500y=325,3000x+2400y=360$$

Subtract 3000x+2400y=360 from 3000x+1500y=325 by subtracting like terms on each side of the equal sign.

$$3000x-3000x+1500y-2400y=325-360$$

Add 3000x to -3000x. Terms 3000x and -3000x cancel out, leaving an equation with only one variable that can be solved.

$$1500y-2400y=325-360$$

Add 1500y to -2400y.

$$-900y=325-360$$

Add 325 to -360.

$$-900y=-35$$

Divide both sides by -900.

$$y=\frac{7}{180}$$

Substitute \frac{7}{180} for y in 50x+40y=6. Because the resulting equation contains only one variable, you can solve for x directly.

$$50x+40\times \frac{7}{180}=6$$

Multiply 40 times \frac{7}{180}.

$$50x+\frac{14}{9}=6$$

Subtract \frac{14}{9} from both sides of the equation.

$$50x=\frac{40}{9}$$

Divide both sides by 50.

$$x=\frac{4}{45}$$

The system is now solved.

$$x=\frac{4}{45},y=\frac{7}{180}$$