If the ratio of x to y is 3 to 7, then (y-x)/(x+y)?  Pick
A) -7/3
B) -3/7
C) 4/10
D) 1
E) 7/3
I believe this problem can be solved using algebra.   The ratio of x to y is 3 to 7 means   (x/y)=(3/7)   Cross-multiply   3x = 7y   x = (3/7)*y   Then, substitute x in the original equation in the problem with the value we just found.   (y - (3/7)*y) / ((3/7)*y + y)   = ((4/7)*y) / ((10/7)*y)   Simplify by canceling the y in the numerator with the y in the denominator.   (4/7) / (10/7)   = (4/7) * (10/7)   The 7s cancel each other out, and you are left with 4/10.
<result>C</result>
If the ratio of x to y is 3 to 7, then (y-x)/(x+y)?