We invite you to test your GMAT knowledge for a chance to win! Each week, we will post a new Challenge Problem for you to attempt. If you submit the correct answer, you will be entered into that week’s drawing for a free Manhattan GMAT Prep item. Tell your friends to get out their scrap paper and start solving!

Here is this week’s problem:

At noon, Adam begins painting a house. Two hours later, Clara begins painting the same house and one hour after that, Wong begins painting the house. Each works without stopping at his or her respective constant rate. In the end, each paints 1/3 of the house. Working together and starting at the same time, Adam and Wong could paint the entire house in half the time it would take Clara to paint the house by herself. How long would it take Adam to paint the house entirely by himself?

To see the answer choices, and to submit your answer, visit our Challenge Problem Showdown page on our site.

Discuss this week’s problem with like-minded GMAT takers on our Facebook page.

The weekly winner, drawn from among all the correct submissions, will receive One Year of Access to our Challenge Problem Archive, AND the GMAT Navigator, AND Our Six Computer Adaptive Tests ($92 value).

18 HOURS.??