Tricky interview question: You have 10 sets of gold bars and only one is defective. How do you work out which one?

A candidate for an analyst position at a private equity firm in Hong Kong was asked the following question…

The question
You have 10 stacks of gold in front of you. Each stack is made up of 10 gold bars. One of these stacks contains defective bars that all weigh 10.1kg, rather than the standard 10kg

You have scales, but you are only allowed to turn them on once and you can only read the weight on the scales once. How do you find out which gold stack is defective?

The candidate’s reply
I could not provide a definitive answer and gave a probability-based reply which did not impress the interviewers.

How he would have responded in hindsight
I should have taken a minute to think it through. I would place on the scales one bar from stack one, two bars from stack two, and so on. Only when the final 10 bars from stack 10 were loaded would I look at the scales.

The decimal point on the scales would indicate which stack was defective – i.e. if all the gold bars weighted 10kg, then the scales would read 550kg. But if stack seven was defective, they would read 550.7kg.

The question is tricky because it only has one solution, but it also allows scope for the interviewer to see your thought process. It was testing my ability to think through a problem and structure it before diving in, and also my ability to juggle numbers quickly. I didn’t get the job.

How would YOU have answered?
Use the comments box below to suggest a better response to the interview question above.

Comments

Post a Comment

Popular posts from this blog

I'm an accountant, I hate my job, but seriously, I wouldn’t know what else to do

I was born to be a lot of things, but being an accountant isn't one of them. In my heart of hearts I have always known this, but for some stupid subconscious reason, I have always ignored it. Why? Well...um...err...I didn’t know what else to do. How many people faced with the same predicament of deciding on a profession upon graduating used “not really knowing what to do” as their guiding compass? Blink. Ten years have passed and you’re left wondering, how did I get here? In this cubicle? Doing something I cannot stand (and I’m not even honestly good at), with people I quite frankly don’t really care about? For me that was accounting, a profession that conjures numerous clichés, such as boring, bean counting, personality not needed, number crunching etc etc. These have now evolved and have been replaced by repetition, reconciliations, long hours, fudging figures, high turnover, Enron and even more reconciliations. R-E-S-P-E-C-T But please don’t get me wrong, I have the utmost respe...
Read more

Three money managers who lived through the 1987 stock-market crash warn of danger today

Image
By  Philip van Doorn Published: Oct 31, 2017 1:49 p.m. ET SHARE   ‘I would take some money off now because ... there are clear signs of deranged valuations,’ says Gabelli fund manager Lawrence Haverty Getty Images A trader on the New York Stock Exchange on Oct. 19, 1987 — Black Monday. When the stock market crashed on Oct. 19, 1987, investors panicked. It was an unfamiliar event — the previous decline of a similar magnitude occurred 58 years earlier, in 1929. Now, 30 years after Black Monday in 1987, there are professional investors still at work who lived through that fateful day. In interviews, three of them talked about their experiences, offered insights into warning signs and gave advice on how to handle major downturns. They are: •  Lewis Altfest , president of Altfest Personal Wealth Management, which manages about $1.3 billion for private clients. Altfest founded the firm in 1983 after working as a general partner and director of research at Lord, A...
Read more

Have We Reached a Top?

By James Kostohryz It's never been my position that the flow of fundamental news would turn from positive to negative overnight and in a total fashion. The world simply doesn't work that way. When I terminated my core long position a couple of weeks ago for reasons explained in�Ten Reasons the Countertrend Rally May Be Over,�I outlined a series of factors I believe may manifest in the later half of 2009 and the first half of 2010. Indeed, most of these factors will be more back-end loaded, as negative factors tend to build on one another and gain momentum in time through the medium of psychology and social mood. It's my view that the flow of economically relevant events�-- and perceptions of these events --are in the early stages of a transition. In this case, a transition means the flow of relatively good news will tend to wane somewhat while there's an uptick in relatively bad news. This is what one would expect at a top. However, it's to be expected that during t...
Read more