1950 AMC 12 Question 29 - thichhoctoan.com

Question 29

A manufacturer built a machine which will address $500$ envelopes in $8$ minutes. He wishes to build another machine so that when both are operating together they will address $500$ envelopes in $2$ minutes. The equation used to find how many minutes $x$ it would require the second machine to address $500$ envelopes alone is:

$8-x=2$
$\dfrac18+\dfrac1x=\dfrac12$
$\dfrac{500}{8}+\dfrac{500}{x}=500$
$\dfrac{x}{2}+\dfrac{x}{8}=1$
None of these answers