From where should we practice Guesstimates and case studies?
Many people struggle with guesstimates in the interviews of non-technical companies.
Guesstimates are no longer in fashion, IMHO. I wonder if companies still ask them. Google used to like them; but they now clearly mention on their recruitment website that 'brain teasers' aren't part of Google Interviews anymore.
Because it's a guestimate, you could memorize two 'routines' to arrive at a specific 'percentage' or a 'number'. For example: Let's say you settle on these steps:
1. 100% | 20% | 5% | 33.33% : You could use this in any situation. For example-
Question: How many Mercedes Cars are there in Pune?
Your Answer: While I do not know the population of Pune, I'd assume that there are about 5 lakh (100%) families in Pune that are in the higher middle class or rich.
Since a luxury car is a status symbol, I'd assume that 20% of these either own a luxury sedan. Which means, we've a total of 1,00,000 sedans in Pune.
Mercedes is quite a popular brand and is often the first name associated with luxury cars. I'd guess that 5% of these cars 1,00,000 are ultra-luxury cars (BMW, Mercedes, Audi etc.). This brings the count down to about 5,000.
Now, I'd say out of these 5000, Mercedes definitely controls a larger market share and my guess would be 33.33% - and my guess would be 1600-1700 Mercedes cars in Pune.
...if you want, you can continue your bullshit to arrive at even more 'believable' number.
Keep in mind that the Interviewer is more interested in finding out your approach; and when you do spread out shit like a boss; they are impressed.
Tip: When a guesstimate is asked, take out your pen and paper and do the math in front of their eyes. It's way more impressive than doing it in your head. You could write and freaking percentage on the paper just to make them believe that you're actually doing something important.
Hope this helps. All the best!