This is postmarket. Here are the top asks
arca 20.19 1000
brut 20.24 800
You place a buy order at 20.25, intelligent. You first get filled 800 shares from brut at 20.24, then the remaining shares from arca at 20.19.
I know, you should place your limit order at 20.19, or go direct to arca. But assume the market is moving too fast to make that kind of decision quickly.
arca 20.19 1000
brut 20.24 800
You place a buy order at 20.25, intelligent. You first get filled 800 shares from brut at 20.24, then the remaining shares from arca at 20.19.
I know, you should place your limit order at 20.19, or go direct to arca. But assume the market is moving too fast to make that kind of decision quickly.