Question 870508
If order mattered, then there are 500*499*498 = 124,251,000 ways to test 3 lightbulbs (from a batch of 500). 



Since order does not matter, we divide by 3! = 3*2*1 = 6 to get 124,251,000/6 = 20,708,500


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Final Answer: There are <font color="red">20,708,500</font> different ways to test 3 light bulbs (from a pool of 500). Order does not matter.