An alloy weighing 16 ounces is 50% gold. How many ounces of pure gold must be added to create an alloy that is 80% gold?  Pick.
A) 24	B) 18	C) 9	D) 27	E) 18

Rationale: "an alloy of 16 oz which is 50 % gold means there is 8 oz of gold . to get to an alloy that is 80 % gold , let ' s use this expression : ( 8 + x ) / ( 16 + x ) = 0.8 with x representing the amount of pure gold that must be added to get to 80 % . the expression we are using represents the new total weight of pure gold over the new total new weight of the alloy and this fraction should represent 80 % or 0.8 . you will see that 24 is the correct answer , as 32 / 40 = 0.8 choose a"
Answer: A