Currency Pair "Out of Line?"

Hi, I’m new to Forex and have a question about the relationship of currency pairs. What reason(s) would there be for a pair to trade “out of line?” That is, the AUD/USD * EUR/AUD should equal the EUR/USD. I noticed a day recently where it was trading off by about a pip and a half consistently all day. Any help on this would be appreciated. Thanks…

just go through school of pipsology. The answer already there for us :slight_smile: