| Topic Name: |
preparation for case interview |
| Message Name: |
answers, sort of |
| Date Posted: |
03/26/2001 |
| In Reply To: |
How do you figure out the answer to the diaper question and the supertanker question? Is it just estimating a ballpark figure, or what? How could anyone expect any precision?
On the round manhole question, is the answer (1) that it can't fall in the hole, or (2) it's easier to remove, since you can roll it off?? |
| Message: |
I'm not sure how many firms are still using the "brainteaser" type questions (like the manhole question, and stuff like "5 ways to measure the height of a building with a barometer"). I went through the entire interview process without any of those. Mostly the interviewers asked real-life case questions. But, answers to the manhole question might also include that they're cheaper to make round, that they are easier to roll down the street (since they're heavy), and any other sensible answer that you might come up with.
As for guesstimates, they are common, but are usually imbedded in a case question (which is how you might be using them on the job, anyway). The answer is less important than the way you figure out the number. Here's a start for the diaper question...
1. 275MM people in the US. Round up to make a nice whole number of 300MM.
2. Figure out a percentage of those who wear diapers... figure ages 1-4 wear them. And guess that 5-10% of the population is in that age bracket (again, try to use whole, easy to multiply numbers to make your life easier... you won't have a calculator!).
3. Figure that each of those goes through an average of 5 per day (infants go through 8+, toddlers 2-3).
4. Figure out the numbers for the year...
Soooo...
300MM ppl x 5-10%= 15-30M diaper-wearers
5 per day x 7d per week = (rounded) 40/week
40/week x 50 weeks/yr (ROUNDING again)= 2000/yr
15-30M x 2000/yr = 30-60B diapers per year
Is that the ACTUAL number? I don't know, and neither will the interviewer, unless they just did the study. What's more important is HOW you arrive at the number.
Also, if you want to shine, add in some extras, like asking the interviewer if they want to include adult diapers also (and just do the same process to figure out that number...), or consider that some small percent of the population uses non-disposable cloth diapers...
Remember, it's not the PRECISION that's being measured, it's the process.
By the way, I had to use a guesstimate in one of my interviews, and was off on one of my assumptions. Although my numbers were wrong in the end because of that mistake, I didn't get points off, because they were more interested in how I arrived at the final number.
You do need to know some numbers, like US population, number of major cities in the US, etc. You can usually find all those numbers in the case study guides (like Vault, etc.).
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