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BLTN
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Let me break down this question in a way that will help you tackle similar problems in the future.
First, choose 300 as the total - it's not random! When dealing with both percentages and fractions, we want a number that works nicely with the fraction (2/3).

So,
-Total: 300 participants
-Drug Group (60%): 180 people

Improved (2/3): 120 people 👍
Didn't improve (1/3): 60 people 👎

-Total improved (70%): 210 people

From drug: 120 people
Must be from placebo: 90 people
-Placebo didn't improve: 30 people

Hence,
x = 120:60 = 2:1 (Drug improved : Drug not improved). In other words 120 is 2 times(x) 60.
y = 120:30 = 4:1 (Drug improved : Placebo not improved). In other words 120 is 4 times(y) 30.

GMAT Tip
Always look for numbers that make your fractions play nice! In GMAT, if you see 2/3 or similar fractions, try multiples of 3 first. It'll save you from decimal headaches!
Hope this helps!
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