# McKinsey Common Case Question

MBB McKinsey
New answer on Feb 24, 2021
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Hello

A common question I faced in 2 of my interviews as I am going through the process and I have not seen covered in any case book or any case on prep lounge is : "what could have happened ..."

Example : Your colleague called you and said we estimated the production capacity at 2000 units per day and we just calculated 2500 units per day, what could have happened and caused this discrepancy ?"

How would you answer this question in a "structured" format ?

P.S.: You do not need the full case for this question.

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Hi there,

This is a great question that really tests your ability to react quickly and think in a structure way!

First tip: If you're struggling to come up with something on the spot, don't hesitate to ask for 10-20 seconds to think about it!

Personally, I can think of the following things:

Estimation Error - i.e. our calculation of 2,000 is wrong

Output measurement error - i.e. their measurement of 2,500 is wrong

Production "glitch" - i.e. some sort of bottleneck built up at the end of a day at the end of the line and was quickly resolved/pushed through the following day

Average vs. distribution/variation - i.e. 2,000 is the average production but production is inconsistent across days (just look at current vaccine production rates by Moderna + Pfizer, or Tesla production rates)

Hello!

It´s a great question indeed.

however, I don´t think we can give a good generic answer, without knowing the intrinsics of each case. I believe good answers are the ones rooted in the problem itself and the info about it that has been previously shared (e.g., your colleague called you and said we estimated the production capacity at 2000 units per day and we just calculated 2500 units per day. This signals how plants have been underutilized so far, due to 3 key factors that we have seen in the problem so far, X, Y and Z.

Hope it helps!

Cheers,

Clara

Actually it was the very first question after structuring, the interviewer caught me off guard with this one. the following question was to estimate the demand increase.