Many teachers who've used Investigations units for a few years have by now come up with a type of annotated teacher's edition of our own. This is because they have written some of the answers in their books as they went through different units and did the problems. They have also written in comments and strategies based on their doing the units more than once.
I know it isn't easy the first time through a unit, especially if you are used to a traditional TE with all of the answers in it. Nevertheless, I'd suggest resisting the urge to copy answers from somewhere else. I think that some of the best things we can do for kids is to model thinking for them by doing actual thinking in front of them and by taking the time to check ourselves to see if an answer makes sense. It is much more difficult to do that and much less likely to happen when you already know the answer to a particular problem.
