A man purchases 2 watches for $ 900. He sells one at 10% loss and the other at a profit of 20%. He neither gains nor loses on the whole. Thus, the cost price of two watches are :  Pick one
A) $ 900 and $ 300	B) $600 and $ 900	C) $900 and $450	D) $600 and $300	E) $550 and $ 350
x + y = 900 --- (1)   0.90x + 0.80y = 900--- (2)   (2) - (1) --&gt; -.10x +.20y = 0   10x = 20y   x/y = 2/1 = (2*300)/(1*300) = 600/300   Answer: $600 and $300
<result>D</result>
A man purchases 2 watches for $ 900. He sells one at 10% loss and the other at a profit of 20%. He neither gains nor loses on the whole. Thus, the cost price of two watches are :