Math algorithm/function to convert this number to 40?

Sure the equation is y = 147.5x – 151.75
Where x is the number that goes from 1.3 to 1.7
And Y is the one that goes from 40 to 90.

If you want it the other way let me know.

Here it is:
y = 0.0068x + 1.0288

Enjoy

How would the function change if the minimum number is -1.3?

I forgot to add the -

Sorry.

No problem. I did it in excel

y = 19.667x + 65.567
or
y = 0.0508x – 3.3339

You mind sharing how you did this in Excel? It would be useful should he ever need to make another range conversion—plus I’m intrigued.

Sure. First, I started to solve the equations mathematically like we learned in 8th grade.

Then I got lazy and decided to check it by making a short table of the four numbers.
x y
-1.3 40
1.7 99
And hit “Insert” “Scatter plot” Then selected “Add Trend line” “Linear” “Show equation”.

I then swapped the two columns and did it again. It took less than 4 minutes.

Just learned a new Excel trick, thanks!