How do I make a value increase as another value decreases - and vice versa

[rayhanmiah]

I need help with a formula that makes a value increase/decrease as another value increases/decreases.
For example:

The sales price of £19.60 is equivalent to 900 monthly sales. For every 10p increase in the sales price, the monthly sales drop by 20.

I've tried inverse proportion which worked a little bit (£19.60 = 900) but when I increased the price to £19.70, it returned the value 895 instead of the expected value of 880.

 

[rayhanmiah]

 

[JimM]

Using £19.60 = 900 sales as your base then

If you put the price into cell A1 your sales will be

=900-((A1-19.6)*200)

 

[rayhanmiah]

Using £19.60 = 900 sales as your base then

If you put the price into cell A1 your sales will be

=900-((A1-19.6)*200)

Thank you so much! I assume it works the same way for everything else?

 

[JimM]

It should do, you'll obviously need to swap out the appropriate numbers