Answer:
(x*(1+a))*0.8 = 400; x = 500/1+a
Step-by-step explanation:
First, increase the number (which we will call x) by a%
x*(1+a) -> You do 1 + a because if you wanted to increase let's say 5 by 20% you would do 5 + 5*0.2 and if you factor that out it becomes 5(1+0.2)
Next, decrease it by 80%.
(x*(1+a))*0.8
Finally, make it into an equation.
(x*(1+a))*0.8 = 400
If you solve it, you get:
x(1+a) = 500
x = 500/1+a
