If x, y, and d are positive numbers such that 10*x/(x+y)+ 20*y/(x+y)=d and if x is less than y, which of the following could be the value of d?
Choose one:
A) 10	B) 12	C) 15	D) 18	E) 30
Answer choice C: d= 15   (10x + 20y)/(x+y) = 15   10x + 20y = 15x + 15y   5y = 5x   y = x   Doesn't work because the problem states that x&lt;y.   We need y to be larger, so let's try answer choice D: d=18   10x + 20y = 18x + 18y   2y = 8x   y/x = 8/2   Success! x&lt;y.   The correct answer is 18.
<result>D</result>
If x, y, and d are positive numbers such that 10*x/(x+y)+ 20*y/(x+y)=d and if x is less than y, which of the following could be the value of d?