I have about 38 old baseball cards, Yogi Berra, Jackie Robinson etc. 5 1/2 long 3 1/2 wide. How much are they worth?

It depends on the make, years, condition, etc.

Get one of those guides that shows the value of all the amounts of cards or just take it to a baseball card store and see how much they will pay you for it. (look in the guide yourself though)

Or you could always try searching on Ebay.