The Let() function creates a temporary holder for a value, called a variable, which can be plugged into a calculation over and over again. You have to do a little more work upfront to set up a variable, but that effort pays off with faster calculations that are easier to read, edit, and troubleshoot.
Frequently Asked Question: No Zero
The Choose() function insists that the first parameter should be for a zero condition. What if I don't want zero? My condition values start with 1.
You're in a common predicament. Luckily, you have two equally easy ways to get what you want from the Choose() function. Perhaps the most obvious is to simply add a dummy zero result:
Choose ( Door ; "" ; "European Vacation" ; "New Car" ; "Wah Wah Wah" )
In this calculation, there's no Door number zero, so you just stick "" in the spot where the zero result belongs. You could just as well put "Death by Boredom" there, since it never gets chosen anyway. Just make sure you put a set of empty quotes there, so your first real result is in the number-one spot.
If you just don't like having that dummy...