Challenge Problem of the Month

Answer correctly to win!

I will choose one person out of all the people who answer correctly to win a free Manhattan GRE Strategy Guide. If you're keen on calculations or on winning free things, you should try your hand this month.

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This Month's Problem: "Original Number"

When a certain positive number is subtracted from 15, the resulting number is 2 times the positive square root of the original number. Which of the following could be the original number?

Indicate all such original numbers.






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