Question

Solve the following system of equations by the substitution method.

10x + 10y = 1
x = y - 3

What is the value of y?

-29/20
31/20
-3/2

Answer 1

they both have to be positive, because a positive number subtracted from a negative number makes the difference negative

Answer 2

you know x = y-3 from the second equation.

plug that into the first and solve for y

10(y-3)+10y=1

Answer 3

\[10x+10y=1\]
so\[x+y=0.1\]
but
\[x=y-3\]
substitute in the above one
\[(y-3)+y=0.1\]
\[2y+3=0.1\]
\[2y=0.1-3=-2.9\]
\[y=-2.9/2=-1.45\]
\[y=-\frac{ 29 }{ 20 }\]