Life In 19x19

I've been playing for quite a while but never put in enough effort to go past DDK. I recently found out the Nihon Ki-in offered a free tsumego app, so I picked it up. One of the problems, though, I just didn't understand why it was included, and I hope I'm not missing something:

Click Here To Show Diagram Code

[go]$$B
$$ | . . . . . . . . .
$$ | . X X X . . . . .
$$ | X O O X X X X . .
$$ | X O . O O O X . .
$$ | . . O O . O X . .
$$ ------------------[/go]

According to the app, the correct answer is:

Click Here To Show Diagram Code

[go]$$B
$$ | . . . . . . . . .
$$ | . X X X . . . . .
$$ | X O O X X X X . .
$$ | X O . O O O X . .
$$ | . 1 O O . O X . .
$$ ------------------[/go]

But doesn't white live thanks to the ko rule?

Click Here To Show Diagram Code

[go]$$B
$$ | . . . . . . . . .
$$ | 3 X X X . . . . .
$$ | X O O X X X X . .
$$ | X O . O O O X . .
$$ | 2 4 O O . O X . .
$$ ------------------[/go]

Black doesn't connect with , he makes a ko threat.

Ah, but black gets a chance to move somewhere else for - he can look for the biggest threat he can find. If W responds then perhaps B doesn't get any points from this "ko threat" directly, but B can recapture the corner, and now W is prohibited from recapturing! If W ignores B's threat to save his corner, then B gets to follow through on his threat, which can be worth a lot of points.

The app is "free" rather than free. It includes just a few sample tsumegos, the rest are for-pay packages. I bought some of them and they are relatively difficult for how they are labelled (the ones that are meant to be done before the "beginner" ones are the ones meant to be done by, well, beginners!).

As others have said, the goal in the one you got stuck on is about creating a ko, not about killing the group, which I feel is already a problem not for beginners the way most of us probably use the term.

I figured it would be used in a ko fight, but I figured that in a "beginner's tsumego" they would make it obvious that there was a situation where a fight could break out over this group since the rest of the problems in this section are about killing or saving groups.

Thanks.

There's kind of an unwritten rule about life and death problems that in killing, your first goal is to kill, or make a ko if you can't do that, or make seki if you can't do that. When trying to live, life is better than seki which is better than ko, but any of those could be the answer if a higher one isn't.

Also, the terms "beginner", "intermediate", and "advanced" are relative. You can be sure that the problems presented by one source of problems to be consistent with the level of difficulty. But you should have no expectation about the relative difficulty of problems from different sources. So look for reviews of the problem sets for that sort of information.

As indicated, it is usual/common that you aren't told what the goal is. You might just be being asked "what is the status?" (alive absolutely, alive in seki, alive in ko, dead). Note that the same configuration of stones might represent a problem of somewhat different level of difficulty (less) were you supplied the additional information of exactly what is possible (the exact goal).