If you use it at a gas station or something I'm sure you'll get away with it. I wouldn't sell it, bills aren't worth much unless they're from some historical even (like say, a bill with JFK's blood on it, or a bill from a huge bank robbery)

However if you have old coins they could be worth a lot. I once sold two old 50￠ pieces (I think from the 50's) for $16. They told us the price could've doubled if we waited a couple more years but we needed the money.

Yes. It's still legal tender, but is probably worth more than $20 to a collector. The only issues would be if there was a currency recall. After that point old money may be worthless. However that hasn't happened in the U.S. in recent times (one exception being in Hawaii in 1942). But in Mexico they recalled the old peso and put out new peso's. So old ones are no longer considered valid money of you had them still.

Sure can. To a collector of old bills, it might be

worth $22.00.

yes

Yep.