I have a deck that is cantelivered off the side of my house the Deck is 4'8" X 21'6". I ere should I place the bolts?noticed that approximately 5 of the 22 joists are rotted at the end and the rot is from about 2 - 8 '' in length. Would it be all right to "sister" on new 2 by 8's . How many bolts should I use and where should the bolts be placed?

So the rotted joists are less than 5' long, right? If you can get under the deck to work I would remove the bad joists totally. If you sister in a new joist it needs to cross the cantilever point and go all the way to the next suuport, in you situation that's likely the house ledger board.

I agree with ballengerb1... would be the best