Wikipedia:Reference desk/Archives/Mathematics/2016 October 30

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October 30

Maths

I have a function that represents price. The cost is 18 per unit. After the 25th unit, shipping is 24+(.25(number of units above 25)). I tried 18x+(24+.25x) but this includes all numbers before 25. How do I graph this function? Seattle (talk) 04:05, 30 October 2016 (UTC)

The function f(x) is defined as follows:

For every x<26, f(x)=18x.

For every x>25, f(x)=18.25x + 17.75.

HOTmag (talk) 17:04, 30 October 2016 (UTC)

(ec) You assumed there is no shipping charge for less than 26 units. I would not assume that.

The function f(x) is defined as follows:

For every x<26, f(x)=18x + ?

For every x>25, f(x)=18x + 0.25(x-25) + 24

This does simplify to the same value you had, but it may help the OP to see the original form. StuRat (talk) 17:36, 30 October 2016 (UTC)

Yes I should have pointed that out to them rather than just leaving them to see that the answer looks a bit silly. Which making a graph should do I hope. My best guess is they meant there to be a shipping charge of 24 if the number of units is 25 or less. Assuming this is all something real. Dmcq (talk) 01:42, 31 October 2016 (UTC)

Why did you add a question mark to the first case, but not to the second case as well? If you don't rule out a shipping charge for less than 26 units, then another person won't rule out a tariff charge for more than 25 units. However, in my view, there is no tariff charge for more than 25 units, nor is there a shipping charge for less than 26 units, because the OP didn't mention any additional charges besides what they did mention. HOTmag (talk) 12:52, 31 October 2016 (UTC)

It's not reasonable to have a shipping charge for a large number of units and yet have none for a smaller number (if you did that, then customers with larger orders would just submit a lot of small orders). Indeed, the opposite is often the case, where the shipping charge is waived only in the case of a large number of units, as a way to give a volume discount. As for tariffs, there are many cases where no separate tariff is charged, which either means there is no tariff, or that it is included in the base price. Here in the US, this is common. StuRat (talk) 20:01, 1 November 2016 (UTC)

If x is less than or equal to 25 then 18x

Otherwise if x is more than 25 it costs 18x+(24+0.25(x-25))

You just had to subtract the 25 to get rid of them. 24 - 0.25×25 gives the 17.75 in the formula just before. Dmcq (talk) 17:34, 30 October 2016 (UTC)

If you are dissatisfied with the two-part answers above, it could be written as one expression:

f(x) = [x<26]18x + [x>25](18.25x + 17.75)

where the square brackets are the Iverson bracket. 208.54.85.156 (talk) 00:47, 31 October 2016 (UTC)

The OP, who is a student majoring in history and political science, will probably be dissatisfied with unfamiliar mathematical notations - like the Iverson bracket, so I guess they will prefer my first answer to your one. However, if they are not satisfied with a two-part answer either, then I would suggest them a one-part answer containing familiar notations only, as the following: $18x+(0.125x+8.875)\left(1+{\frac {|x-25.5|}{x-25.5}}\right)\cdot$ HOTmag (talk) 11:15, 31 October 2016 (UTC)