These last few days I've been hammering the quant questions available through the forums on http://www.gmatclub.com/ - lots of fun (!). Was stumped by one particular combination question that asked:

"

*There are three secretaries who work for four departments. If each of the four departments has one report to be typed out, and the reports are randomly assigned to a secretary, what is the probability that all three secretaries are assigned at least one report?*"

What had me really stumped was that once I thought I had the answer, it was significantly different from the OA. As the OA looked a bit dodgy, I thought I'd trawl google for suggested solutions and answers and was somewhat dismayed to find a number of different answers posted by various tutors and quant-proficient individuals.....

Being something of an excel geek, I then decided to check this out long-hand myself.... as I thought, the OA offered in the gmatclub download was wrong. Nevermind, the combinatronics document is otherwise a good resource and my the learning experience has been enriched somewhat by having to prove why my thinking was right :) :) here's my final answer ......

Spoiler: There are 3^4 (or 3*3*3*3) possible combinations = each option therefore is 1/81.

You then choose 1 of three secretaries (3C1) to receive two reports (4C2), and then work out the number of permutations to assign the remaining 2 reports to the 2 remaining secretaries (2P2).

3C1 * 4C2 * 2P2 = 36

Answer: = 36/81 = 4/9

Now it's time to cycle down to the lake, enjoy the sunshine and run through some DS problems.

Hi Chris,

ReplyDeletegreat to see a fellow blogger working for a fall 2012 mba admit. Best of luck with the GMAT :)

http://pyarapopat.wordpress.com

Thanks! Working on the quant these days as my first official attempt went alright on Verbal - I hope another month or so doing the daily questions and focusing on tougher DS and combination sections will bring the quant score up to around 45 (pushing well into the 700+ region) and then I can concentrate on apps :)

ReplyDeleteSeems like a good plan ... when is your GMAT date ?

ReplyDeleteNot booked just yet - I'm not in too much of a rush as the test centre is nearby and there are lots of spaces even at short notice.

ReplyDeleteCan't sit it until the 3rd week of May anyhow because of the last one :)