shares of stock (GMAT Prep)

[alex.gellatly]

John and Mary own shares of stock in a certain company. Does John own more shares of the company's stock than Mary?

1. Mary owns more than 500 shares of the company's stock.
2. The number of shares of the company's stock that John owns is 400 less than twice the number of shares of the company's stock that Mary owns.

[spoiler]Why is it not B?[/spoiler]

[Anurag@Gurome]

John and Mary own shares of stock in a certain company. Does John own more shares of the company's stock than Mary?

1. Mary owns more than 500 shares of the company's stock.
2. The number of shares of the company's stock that John owns is 400 less than twice the number of shares of the company's stock that Mary owns.

Say, Mary owns M shares and John owns J shares.

Statement 1: We have no idea about the number of shares owned by John.

Not sufficient

Statement 2: J = (2M - 400)
Only from this information we cannot say whether J > M or not.
To show with example, consider the following two cases,

• J = 100, M = 250 ---> J < M
  J = 600, M = 500 --> J > M

Not sufficient

1 & 2 Together: If M < J, then M < (2M - 400) ---> M > 400
As M > 500, M is always less than (2M - 400) or J

Sufficient

The correct answer is C.