No offense to anyone here, but this topic is pretty ridiculous. There is no set number of aliens needed to take down an elder because we don't know a canon elder's capabilities. At all. For all we know a real "elder" could be so battered up and crippled from countless fights that it only carries the respect of the other predators, nothing more.
Even if we did know its abilities, the concept of exhaustion comes into play. An elder could NEVER take down 1,000, not even 100, xenomorphs in melee combat because it would simply tire. In addition, it doesn't matter HOW good a fighter you are if you are being struck from all sides at once!
Obviously at a range ANY predator has an edge, giving a set number of aliens to be blasted to bits by a ranged weapon is rather pointless.
Deathdrop is right when he says that it all depends on the scenario. It's like asking, "How many licks does it take to the Tootsie Roll center of a Tootsie Pop?"
The world may never know.
"If anything in this life is certain, if history has taught us anything, it is that you can kill anyone." - Michael Corleone