Hi All,

The speed and ease with which you handle this DS question will likely be based on how you organize your information. You can 'set up' this question using percents, fractions or decimals (depending on whatever 'format' you think is easiest to deal with).

We're told that an investor owns a variety of shares of stock:
1) 30 percent are shares of Company X stock
2) 1/7 of the REMAINING shares are shares of Company Y stock.

This means that we can organize the shares into 3 categories:
1) Shares of Company X (30% of the investor's shares)
2) Shares of Company Y (1/7 of 70% = 10% of the investor's shares)
3) Shares of Other Companies (the remaining 60% of the investor's shares)

We're asked for the number of shares of Company X stock that the investor owns.

Fact 1: The investor owns 100 shares of Company Y stock.

Since these 100 shares represent 10% of the investor's shares, then the TOTAL shares = 100(10) = 1,000. Since 30% of the TOTAL shares = Company X shares, we know that (30%)(1000) = 300 is the number of shares.
Fact 1 is SUFFICIENT

Fact 2: The investor owns 200 more shares of Company X stock than of Company Y stock.

This Fact helps us to create the following equation:

(30%)(Total shares) = (10%)(Total shares) + 200
(20%)(Total shares) = 200
Total shares = 1,000

Again, we can calculate the total shares of Company X stock = (30%)(1,000) = 300
Fact 2 is SUFFICIENT

Final Answer:

GMAT assassins aren't born, they're made,
Rich
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Attached is a visual that should help.