london 3 day pass is it worth buying

Probably not, but you'll have to do the math on admissions for what you want to see to be sure.

What are the sights you want to see in London?

If the Pass is less expensive than the cost of those attractions (add them up), then buy it.

If you are wanting to see a lot of museums while you are there, many museums are free.
So you don't need to pay at all for these.

Depends on what you want to see, but enough of the museums in London are free that you can probably fill three days. Don't worry, you'll need the money to eat... London is crazy expensive.

You're thinking that it will save time, but take a close look at the attractions that are included in the pass. There aren't very many of the major sights for which you get "skip the line" privileges. Then consider how much time you have, and what it will take to get from one of those places to the other. You might find that you won't be able to fit in very many. Skip the Oyster Visitor card option as well, as the regular pay as you go Oyster makes more sense.

Thanks for all the suggestions. appreciate your input. oyster pay as you go card sounds good to me. riverboat and art museums is all I am
interested in. my sister may want more. She is younger.
cm

With so much you can do in London that is free, why would you pay £91 for 3 days. Consider The Tower, The Abbey and St Paul's by all means.

http://www.visitlondon.com/things-to-do/sightseeing/london-attraction/museum/free-museums-in-london

...riverboat and art museums is all I am interested in...

All the art museums are free. The river boat takes the same Oyster card you will buy for the tube and bus. Just tap the Oyster card on the pad when you get on the river boat. Always use the Thames Clipper river boats because they are the only ones who take Oyster card, and the ride is the cheapest. The best in my opinion. Blue and white modern streamlined boats with refreshments (soft drinks), bathrooms on board, comfy seats.
http://www.thamesclippers.com/

...my sister may want more. She is younger...

Don't buy the Pass. Just walk up to the attraction she wants to go to, pay, and go in.

If you do not know how to buy the Oyster card once you get to London, say so, and we will tell you how to do this.