**MGMAT Challenge Problem of the Week**

**10/26/09**

**Machines A, B, and C**

Machines A, B, and C can either load nails into a bin or unload nails from that bin. Each machine works at a constant rate that is the same for loading and for unloading, although the individual machines may have different rates. Working together to load at their respective constant rates, machines A and B can load the bin in 6 minutes. Likewise, working together to load at their respective constant rates, machines B and C can load the bin in 9 minutes. How long will it take machine A to load the bin if machine C is simultaneously

__unloading__the bin? (A) | 12 minutes |

(B) | 15 minutes |

(C) | 18 minutes |

(D) | 36 minutes |

(E) | 54 minutes |

I think the answer is C. I don't think my method is long, but I do think I took a little extra time to think up of the process (again, cos I doubted my concept clarity a little, and so didn't quickly start to solve it the way I was thinking...tried applying formula first, but what good is that if I don't know the concept extremely well?). I'll wait till tomm for them to give the right answer, as well as their explanation. Then I'll compare my answer with theirs.

*Edit:*The OA is C.

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