IMO: D
If x (with x is not zero)is the reciprocal of y, then x*y = 1
A: x / (1/y) = x * (y/1) = x*y = 1 --> eliminate
B: (1/x) / y = 1/(x*y) = 1/1 = 1 --> eliminate
C: (1/y) / x = 1/(y*x) = 1/1 = 1 --> eliminate
E: y/ (1/x) = y* (x/1) = x*y = 1 --> eliminate
D remains as the correct answer choice.
D: (1/x) / (1/y) = (1/x) * (y/1) = y/x = 0.5 --> possible
I think the tips here is:
A & E are the same: x/(1/y) = y/(1/x) = x*y
but A is equal to 0.5 and E is equal to 2. => Both incorrect.
B & C are the same: (1/x)/y = (1/y)/x = 1/(x*y)
but the results of B & C are not the same => Both incorrect.
"There is nothing either good or bad - but thinking makes it so" - Shakespeare.
