If xy > 0, 1/x + 1/y = 4, and 1/xy = 6, then (x+y)/2 = ?	Choose the correct answer:
A) 1/25	B) 1/6	C) 1/5	D) 1/3	E) 6
(1/X+1/Y)=4 canbe solved as {(x+y)/xy}=6. Substituting for 1/xy=6, we get   x+y=4/6   ==&gt; (x+y)/2= 4/(6*2)=1/3.   1/3
<result>D</result>
If xy > 0, 1/x + 1/y = 4, and 1/xy = 6, then (x+y)/2 = ?