Board Thread:Game Discussions/@comment-25184030-20140618223249/@comment-24829740-20140620170525

Well its 11 gems per boss summon, right? So go with 44 and you can get 4 extra kills at 2 items per kill = 8 items. Which means you need 100 total items, minus 8 = 92. You get 50 on the first 15 kills, so 42. Average about 1.5 drops per kill so thats 28 kills past 15, or 43 total EB kills (outside of summoning). That puts you at the gold reward tier (5 keys, 30,000 gold).

I thought that I had read that 43 EB kills was supposed to be enough for EB+ without spending gems, so maybe that 1.5 drops per kill is wrong...

Assuming it is 2 instead of 1.5, that revises to 21 kills, plus the 15 equals 36 total kills, which is 1 over the silver reward tier.