You probably won't get an answer on this, as games rarely give out exact drop rates. Destiny isn't going to be an exception to this, no matter what people complain about. Its like those people complaining about running strikes for 16 hours and not getting an exotic. Or getting one. Assuming 15 minutes per heroic (lol), 16 straight hours at a set rate is 64 strikes. Assuming a 1% drop rate, you on average will get .96 exotics with a three of coins. With a 2% drop rate you'll get 1.92. This is all average. But with a 1% drop rate, doesnt mean you arent going to get 5 in a row, and with a 2% droprate, doesnt mean you wont have to gring out 300 before you see one.