One of my favorite Quantitative Comparison strategies is called "Looking for Equality" (free video on this topic here: http://www.greenlighttestprep.com/modul ... on?id=1099).
In this strategy, I first look for values of x and y that make the two quantities are equal. This often involves checking some easy numbers like 0, 1, -1 etc.

Consider these two cases:
Case #1: x = 1 and y = 1100
Notice that these values satisfy the given conditions that 100 x < y and 1000x < 2y
Now check the quantities:
Quantity A: 1100x = (1100)(1) = 1100
Quantity B: y = 1100
Since the two quantities are EQUAL, the correct answer is EITHER C or D

Now try some other values of x and y:
Case #2: x = 1 and y = 1200
Notice that these values satisfy the given conditions that 100 x < y and 1000x < 2y
Now check the quantities:
Quantity A: 1100x = (1100)(1) = 1100
Quantity B: y = 1200
Since the two quantities are NOT EQUAL, the correct answer is

Cheers,
Brent