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

10x+10y=1
x=y-3
10(y-3)+10y=1
10y-30+10y=1
20y=31
y=31/20

Answer 2

By substitution method, we can substitute the lower equation to x of the top equation as follows:

10 (y - 3) + 10y = 1

Then, we solve for y

10 (y - 3) + 10y = 1
10y - 30 + 10y = 1
20y = 31
y = 31/20 <------ second option