Hello guys, I started learning Mathematica quite recently and I'm amazed by the possibilities of this software! Despite my genuine enthusiasm, I recently encountered a barrier (probably like most of users at the beginning). To most of You my problem surely will be trivial, but it is quite a headache for me. The case is a bit complicated so I will simplify it, so that I can just get an Idea how to get started and then I can develop the code without bothering You too much. Here it is - I would like to write a function that would process a list, with let's say 3 elements, and also return a list with the same number of elements. I guess the beginning should look like this:

The next step should be to check which elements of the input list are numbers - if a and b are numbers and c is string (for instance a letter) the function returns {a,b,a+b+1}, if b and c are numbers, the function returns {b+c-1,b,c} and if a and c are numbers, the function returns {a,2*(a+c),c}. If there are less than 2 numbers in the list, the function should return the original list. 

I know it seems easy, but I have still just a little knowledge about Mathematica language. I assume that I should use If[] and NumberQ but don't know how to put them together. Sorry I don't enclose any code, but all my efforts ended with error messages or a disaster. I also couldn't find any similar example in any of the tutorials or books I read. 

Thanks for Your help and every piece of advise You are ready to share!