Great forum. Lots of good info.

I'm trying to determine the cost basis of some stock I own. My dilema centers around multiple share blocks(different purchase dates) that were lumped together and "converted" at an odd ratio to another company's stock due to an acquisition.

Example: I owned 100 shares of ABC that were purchased at 3 different times in lots of 20, 30, and 50(diffenent $/share each time). ABC was later purchased by XYZ and my shares were converted - 4 shares ABC = 1 share XYZ - so I got a total of 25 shares of XYZ(100/4). If the blocks had been converted individually, I would have received 5 (20/4) + 7 (30/4) + 12 (50/4) = 24 shares and some cash from the partial shares from the 30 and 50 share blocks.

So my real question is how do I determine the basis for the one share that is really a combination of the 30 and 50 share original purchase? Thanks for any help with this.