Nathan B. answered • 03/31/15
Tutor
5
(20)
Elementary and Algebraic skilled
2x + 3y = 25
4x - y = 15
4x - y = 15
Substitution means that we need to isolate a variable and use that in the other equation. We have a 2x, a 3y, a 4x, and a -y. That -y will be the easiest since it has the easies coefficient to deal with--a negative one.
4x - y = 15
-y = 15 - 4x
y = 4x - 15
Now that we have a value for y, we plug it into the other equation:
2x + 3(4x - 15) = 25
2x + 12x - 45 = 25
14x - 45 = 25
14x = 70
x = 70/14
x = 5
Now that we know x, we can solve for y:
y = 4 * 5 - 15
y = 20 - 5
y = 5
Now to check our answer:
2 * 5 + 3 * 5 = 25
10 + 15 = 25
25 = 25
