Mike's electricity use this year decreased by 22% from his electricity use last year, u. Write an expression for his electricity use this year in terms of u.

Answer 1

If u was last year's use and it decreased by 22%...

u - 0.22u

Now, that would combine to be 0.78u, but we are asked for an expression and not a term.

Answer 2

If last year's electricity usage is u, and this year's usage is, say,w, the a decrease of 22% would be found as follows:

(w - u) / u = -22%

Solving for w,

w - u = -0.22u

w = u - 0.22u

w = u(1 - 0.22)

w = 0.78u