I dont understand this question. Equilibrium Set - Supply and Demand

[Jto_012]

Hi There,

I would like to ask if anyone can tell me how do you solve these equations? Why do you have to multiply the first one by 2, and then subtract it from the second one?

Appreciate it if you can help me understand the concept

 

[blamocur]

Hi There,

I would like to ask if anyone can tell me how do you solve these equations? Why do you have to multiply the first one by 2, and then subtract it from the second one?

Appreciate it if you can help me understand the concept

You do this to transform 2 equations with 2 variables into 1 equation with 1 variable, which is easier to solve

 

[Jto_012]

You do this to transform 2 equations with 2 variables into 1 equation with 1 variable, which is easier to solve

Thank you! I got it now

 

[skeeter]

The process is called “elimination”

[imath]2(q+5p=40) = 2q+10p=80[/imath]

subtract the above equation from the other …

[imath]2q-15p=-20[/imath]
[imath]2q+10p=80[/imath]
———————————
[imath]-25p = -100[/imath]

note the variable “q” is eliminated, allowing one to solve for p.
the solution for p may then be substituted into either of the original equations to find q