msgreen

i'm working on applications for a summer position, and need 2 referees for most of the positions i'm applying for. I know I have one great letter lined up, but I was working on getting a second over the holiday break. I asked a professor in my field, who I had a class with last fall, before Christmas. I hadn't heard from him by the end of the winter holidays, so I asked a second professor, who i had a class with in a tangential field but who I know a little better than the first professor that I asked. She promptly responded and was happy to write me a letter, which was great until I heard back from the first professor. He told me he would be willing to write me a letter, but requested a meeting before he started working on it and mentioned that he will also be writing letters for other students he knows better so he will be relatively busy. I think I'm more confident in the letter the professor who responded a few days ago will write for me, but how do I tell the professor who just responded I no longer need the letter I asked him for? I don't want to impose unnecessary work, but I also don't want it to seem like I don't value his willingness to get to know me and write me a letter. Should I use his letter for the few positions that say they accept a third letter? thanks!