80,40,20,_,5

What’s the pattern?

x=1

Step-by-step explanation:

We are going to use the matching method, it consists in clear the same incognits in both equations and macth those results. Steps below:

First equation:

-2.4x-3.6y=1.2

-3.6y=1.2+2.4x

y=(1.2+2.4x)/(-3.6)    

Second equation:

2.4x+1.2y=1.2

1.2y=1.2-2.4x

y=(1.2-2.4x)/(1.2)

Now we have to match both equations and clear the incognit x

(1.2+2.4x)/(-3.6) = (1.2-2.4x)/(1.2)

(1.2+2.4x) = (1.2-2.4x) *(-3.6)/(1.2)

1.2+2.4x = (1.2-2.4x) *(-3)

1.2+2.4x = -3.6+7.2x

2.4x-7.2x = -3.6-1.2

-4.8x = -4.8

x = (-4.8)/(-4.8)

x = 1