Name range in formula

[MyLe_jam]

English isn't my first language so sorry in advanced.
Hi, I'm using Excel 2016. My teacher use the name range in NPV formula but somehow I can't use it at all.
In details: my teacher name 2 range, each has 15 values, "benefit" and "cost" respectively. Then she use this exact formula "npv(rate,benefit-cost)" and the result was right. But when I use it the formula only calculate the first value in the string of value.
Therefore I can't use formula like "npv(rate, benefit*(1-%change)-cost)" like she did to evaluate changes.
I have attach photos example, unfortunately I dont have photos of my teacher's work
Can anyone explain to me why and how I can fix it, much appreciate.

[#2]

@MyLe_jam 

Instead of images, is it possible for you to post the actual spreadsheet you have? My suspicion is that you haven't actually named the range but have just put a heading up there....but without the spreadsheet itself one can only guess.

[#3]

@mathetes thank you for answer.

Here's an example

[#4]

@MyLe_jam 

I think what you were missing is the absolute reference for the Rate portion of the formula. I didn't check the results but see if this works.

=NPV($B$2,@benefit-@cost)

The "$" dollar signs make each formula, all the way down the column, continue to refer to B2 even though the other references are changing.

[#5]

@mathetes thank for the advice, I tried it but sadly it didn't work.

The formula npv(rate, value1, value2,...) in itself only accept one "rate" so $ is unnecessary, that why I'm convinced the problem lied in name range.

[#6]

You were right. I hadn't used NPV before. THis morning I looked at this resource and learned how it's to be used. You would benefit from the same. https://exceljet.net/excel-functions/excel-npv-function

The way to name that range is to highlight cells D4 through D13 and then use "Insert....Name...Define" from the main menu.

The resulting formula then can read =NPV(B2,ben_cost)  or it could just as effectively read =NPV(B2,D4:D13)

I highly recommend reading that ExcelJet reference, however. It explains well the limitations of the NPV function as well as showing how to use it.