Solve the system of equations by the substitution method.

0.07x – 0.01y = 2.3
0.28x + 0.13y = 17.7

the substitution method says:

1. take one of the 2 equations and solve for x in terms of y or y in terms of x.
2. plug this value into the other equation.
3. plug that value into one of the other equations.


lets multiply everything by 100 to get rid of the decimals.

7x - y = 230

and

28x + 13y = 1770

start with the first equation.

solve for y in terms of x.

-y = -7x + 230

y = 7x - 230

now plug this into the second equation.

28x + 13y = 1770

28x + 13 (7x - 230) = 1770

28x + 91 x -2990 = 1770

119 x - 2990 = 1770

119 x = 4760

x= 40.

now plug this into one of the equations

7x - y = 230
7*40 - y = 230

280 - y = 230

-y = -50

y = 50

so, the solution to this system of equations is x = 40 , y = 50 or the ordered pair (40, 50).

Standard form: 7/100x-1/100y=2.3; 7/25x+13/100y=17.7;
substitute/eliminate x = +1/7y+230/7
substitute/eliminate y = +50
Solution: x = 40; y = 50;
or (x, y) = (40, 50)