A computer computer monitor as regular priced at 3:20 during A2 Day Sale the price was decreased to 2:40 what is the percentage decrease

You're looking for the percentage in decimal form in the equation. We'll call it x for right now. So whatever x is it will be multiplied to 3.20 and subtracted from 3.20 to equal 2.40. So, our equation will look like this

3.20-x (3.20) = 2.40

subtract both sides of the equation by 3.20 to get

-x (3.20) = 2.40-3.20

-x (3.20) = -.80

now divide both sides of the equation by - 3.20 to single out x on the left side

x = -.80/-3.20

x=.25

to turn this back into a percentage, we move the decimal to the right 2 places

.25=25%