In Destiny you can collect three different types of engrams that randomly appear after defeating and enemy. The green ones are uncommon, the blue ones are rare, and the purple ones are legendary. What is the actual percent chance of an engram dropping from a defeated enemy and what is the chance of getting a legendary item from a blue engram and an exotic object from a legendary engram?
Nobody really knows and it is known to change. As I noticed, higher level enemies drop blue and purple engrams more often. Though on a standard earth/moon patrol you should get 1 blue engram from around 200 kills, so 1/200 or .5% approx. With purple engrams i am not sure. I get them quite rarely. I could have a tip to around: 1/2000 or .05%. And with green engrams, you get about 1/50 or 2%
All is approximate though. It might be variable and Bungie seems to keep it as secret.