Math on a sliding scale

Question

I am trying to do a simple calculation for the following:

The phone model has a maximum selling price of GBP 85.00, and this is only with the purchase of 1 unit and a minimum selling price of GBP 50.00 - this is if 150 units or more are purchased in one.

How can I work out a way to price if you buy from 2 to 149 units?

Thanks B.

Answer 1

Formula

Y = 50 + ((85 - 50) / (150 - 1)) * (X - 1)

Result:

X = 1    -->   Y = 85
X = 33   -->   Y = 57.52
X = 150  -->   Y = 50

Answer 2

You probably do not have a linear model in such situations. I do not know the correct English term, but you would be more like a piecewise or step function.

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