What is the best way to handle multiple To and From ranges?

Question

Our users need to specify multiple ranges of quantities and specify a price for each range. I can't post an image or I would show this concept mocked-up.

My question is: Imagine the user is able to specify a quantity of 10.5 (maybe it's a software license for 10.5 years)...what is the price?

Some would argue that the ranges should be:

• From 0-10, my price is $50.
• From 10-15, my price is $40.
• From 15+, my price i $30.

But, then what if my quantity is exactly 10?

What is the best way to handle ranges like this, assuming the user can enter decimal values for the quantity, but also avoiding having to require the user to enter 0 to 10.99, 11 to 15.99, etc?

Answer 1

I suspect you might be misunderstanding the business logic here. Let's take your first example. Under those prices if I buy 10 units, I expect to pay $50 * 10 = $500 (+tax :). What if I order 12 units instead? Would it be $40 * 12 = $480? If yes, then no reasonable person would ever order 9 or 10 units — ordering 11 is cheaper!

However this is not how that price schedule is typically interpreted. Usually, the range 11–15 at price $40 means that any unit ordered ON TOP the first 10 will have the price of $40. Thus, if I'm ordering 12 units I'll have to pay $50 * 10 + $40 * (12 − 10) = $580. And if I order 10.5 units I'll have to pay $50 * 10 + $40 * (10.5 − 10) = $520.

If you use these rules, there is no real ambiguity at q = 10. It will cost $50 * 10 + $40 * (10 − 10) = $500.

Answer 2

Taking the above example, I cannot think of a scenario which in which 10.5 could be required but if it had to be, your increment/decrement controls must have a 0.5 as the "step value". But here another question could be what about 10.25 - 10.75 OR 10.33 - 10.66? For situations like that, you cannot have concept of range (1.25 to 7.44) but rather use exact value model for ordering (6.44)

BUT if you were looking to use a combination of range and discounts, you might want to use something similar.

Answer 3

Unless you are going to add non consecutive ranges why not just remove the "From" value:

^{download bmml source – Wireframes created with Balsamiq Mockups}

Answer 4

Your UI layout is sufficient for integer quantities, but not for float values. For the latter, you should use

From      To       Price
      x < [   10]  $[   50]
10 <= x < [   15]  $[   40] 
15 <= x            $[   30]

in the back-end UI. Of course, this can be expressed less mathematical, but you get the idea of it.

Answer 5

You could write: "From (Incl.)" e "To (Excl.)"

In the BackEnd UI there are three columns: From, To, Price. I am suggesting to call them: From (incl.), To (excl.), Price. In this way the user knows that the first row, for instance, would be 0<= Quantity< 10 and so on.