I need to make a cake that will serve 40-45. Will a 10" and 7" serve that many. The charts that I've looked at seem to think it will, but I'm not sure. Each tier is 4" tall. What do you think?

As I rememver a 10x4 round serves 35=39 and a 7 should give you another 10=14,
That's with servings of 1x2x4. It will be close because you don't know how it iwll be cut.

I get about 45 party servings, thats inbetween earlenes(40), and wiltons wedding serv(5. So, you would be 40'ish in my eyes. It does depend on size, of course. If there is something besides cake and you are instructing in cutting , then you'll be OK. IF not, might be close. I always go over a bit anyways, but always have leftovers. I dont like to cut it close...pardon the pun...LOL
Not everybody eats cake as well.
Blessings~