An alloy weighing 48 ounces is 25% gold. How many ounces of pure gold must be added to create an alloy that is 40% gold? Pick:
A) 15 B) 20 C) 12 D) 14 E) 7

Rationale: an alloy of 48 oz which is 25 % gold means there is 12 oz of gold . to get to an alloy that is 40 % gold , let ' s use this expression : ( 12 + x ) / ( 48 + x ) = 0.40 with x representing the amount of pure gold that must be added to get to 40 % . the expression we are using represents the new total weight of pure gold over the new total weight of the alloy and this fraction should represent 40 % or 0.4 . you will see that 12 is the correct answer , as 24 / 60 = 0.4 choose c
Answer: C