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Before bschool starts, I want to study for case interview questions so I can get a headstart. I don't think I will have much time to prep for this once the school starts. I will post a question here, and if others want to provide their answers/explanations/logic, feel free to do so.

Case Q Stats: Total # of Q's Correct Terp26: 2 isa: 2 BearStearner: 1 Solaris1: 1 Zoinnk: 1

Quote:

Question: 2 Gallons and Unlimited Water

You have a 3 gallon container and a 5 gallon container. If you have access to unlimited amount of water, using those 2 containers ONLY, how can you measure 4 gallon of water EXACTLY?

You have a 3 gallon container and a 5 gallon container. If you have access to unlimited amount of water, using those 2 containers ONLY, how can you measure 4 gallon of water EXACTLY?

My logic: (feel free to critique me, but be gentle )

1) Fill up the 3 gallon container in full 2) Dump all the water from 3 gallon container into the 5 gallon container 3) Fill up the 3 gallon container in full again 4) Dump all the water from 3 gallon container into the 5 gallon container until the 5 gallon container is filled to its capacity (remember, it had 2 gallon capacity left) 5) Now your 3 gallon container should only have exactly 1 gallon left in the container 6) Empty out your 5 gallon container 7) Dump 1 gallon of water from 3 gallon container to 5 gallon container. 8) Fill up 3 gallon container to its capacity again and dump it into 5 gallon container 9) Result should be exactly 4 gallon of water in the 5 gallon container.

Note: I am assuming that there isn't a drop of water wasted during the transfers mentioned above

You have a 3 gallon container and a 5 gallon container. If you have access to unlimited amount of water, using those 2 containers ONLY, how can you measure 4 gallon of water

My solution:

1) Fill up 5 gallon container. 2) Empty it into 3 gallon container. You now have 2 gal left in the 5 gallon container. 3) Empty 3 gallon container. 4) Transfer the 2 gallons from the 5 gal container into the 3 gallon container. 5) Fill up the 5 gal container. 6) Empty the 5 gal container into the 3 gallon container. You now have a 3 gallon container that's filled and 4 gallons left in the 5 gallon tank.

Assumptions: - no water lost between transfers - unlimited refills of containers

Not sure if this is same logic as above....too lazy to think through it but here goes:

1) Fill up 5 gallon tank full and empty it into the 3 gallon tank. This leaves 2 gallons left over in 5 gallon tank and 3 gallons in 3 gallon tank. 2) Empty 3 gallon tank. 3) Fill the 2 gallons from the 5 gallon tank into the 3 gallon tank and fill 5 gallon tank full. 4) Now the 3 gallon tank has 2 gallons, but room for 1 gallon left. And you just pour the full 5 gallon tank into he 3 gallon tank just enough to fill that extra gallon. Now the 5 gallon tank is left with 4 gallons.

A local university's dining services staff has gone on strike. As a result, a popular local coffee shop has seen a recent surge in business as students look for alternative sources of dining. However, since the beginning of the strike, the coffee shop's profits have actually declined. Why is this? How would you fix this problem?

Also a point to note -- I did MC recruiting during college. Probably did 15-20 interviews total. I never once received a brainteaser case question. I really only got business cases like the above.

Because the students have switched from buying higher margin coffee more often to lower margin snacks et cetera that might serve as dinner? That might explain higher sales, but lower profits?

Because the students have switched from buying higher margin coffee more often to lower margin snacks et cetera that might serve as dinner? That might explain higher sales, but lower profits?

I don't know, I'm new at this.

overcrowding by students buying low margin products have turned away the stores older clientele that buy higher margin items

ok, since ninkorn doesn't want to do business cases. this is one i got during a hedge fund interview:

you are throwing 3 darts at a spinning ball (perfectly spherical). each dart has a 100% chance of hitting the sphere. What is the probability that all three darts land in a single hemisphere (any hemisphere) of the ball?

ok, since ninkorn doesn't want to do business cases. this is one i got during a hedge fund interview:

you are throwing 3 darts at a spinning ball (perfectly spherical). each dart has a 100% chance of hitting the sphere. What is the probability that all three darts land in a single hemisphere (any hemisphere) of the ball?

Assuming you get all the darts on the ball, wouldn't they always be in the same hemisphere?

Because the students have switched from buying higher margin coffee more often to lower margin snacks et cetera that might serve as dinner? That might explain higher sales, but lower profits?

I don't know, I'm new at this.

overcrowding by students buying low margin products have turned away the stores older clientele that buy higher margin items

Both solaris and terp26 got the gist of the idea.

To do this properly during a case interview, though. You need to talk through the problem in a structured manner. So the way to do this in a case interview is say something like this.

Well, there are three buckets of reasons that profits can decline: 1. Lower sales 2. Higher costs 3. Product/sales mix shift (Or a combination of the three)

Let's investigate all three. [Now you would ask questions to the interviewer] 1. Has the shop's revenue gone down despite the new business? [In this case, the interviewer would probably say no or tell you it doesn't matter] 2. Moving on, have the costs of the shop gone up? Maybe it takes more people to serve the extra people? [In this case, the interviewer would probably tell you that yes, the costs have probably gone up, but those costs are negligible] 3. OK, then there must be a product mix shift. Perhaps customers are buying lower margin products? [Most likely, the interviewer here would push you further and get you to zero in on the specific problem, but you've essentially cracked the case at this point]

So the specific answer in this case was... The coffee shop was selling very high margin drinks before the strike. After the strike, people have started using it as a diner, and food such as sandwiches are very low margin. Hence, the lower profits.

Depending on the firm, the case would either be over at this point. Or the interviewer may ask you to brainstorm ways of solving the problem. Again, doing this in a structured manner is the key -- revenue, costs, product mix: 1. How do you increase revenue w/o raising costs? 2. How do you decrease costs w/o lowering revenue? 3. How do you drive customers to higher margin products?

This is one I had on an interview with Morgan Stanley's Mortgage Backed Securities Division out of college. (Thankfully I didn't get the position)

Answer , yes or no, and why.

If you stacked quarters from the street level to the very top of the empire state building, would all those quarters fit into this 10 X 10 foot office?

You are in a room with three light switches. Each controls one of three light bulbs in the next room. You must determine which switch controls which bulb. All lights are off. You may flick only two switches and enter the room with the light bulbs only once. How would you determine which switch controls which light bulb? _________________

You are in a room with three light switches. Each controls one of three light bulbs in the next room. You must determine which switch controls which bulb. All lights are off. You may flick only two switches and enter the room with the light bulbs only once. How would you determine which switch controls which light bulb?

Turn two light bulbs on. Wait for awhile. Turn one of them off.

Then you have a warm one, an off one, and an on one.

You are in a room with three light switches. Each controls one of three light bulbs in the next room. You must determine which switch controls which bulb. All lights are off. You may flick only two switches and enter the room with the light bulbs only once. How would you determine which switch controls which light bulb?

Answer:

Turn one light bulb on for about twenty minutes. Then turn it off. Turn another switch on. Then enter the room and feel the two bulbs that are off. The hot one will be attached to the switch that you just turned off.

Case Q Stats Update: Total # of Q's Correct Terp26: 2 isa: 2 BearStearner: 1 Solaris1: 1 Zoinnk: 1
_________________

ok, since ninkorn doesn't want to do business cases. this is one i got during a hedge fund interview:

you are throwing 3 darts at a spinning ball (perfectly spherical). each dart has a 100% chance of hitting the sphere. What is the probability that all three darts land in a single hemisphere (any hemisphere) of the ball?

Assuming you get all the darts on the ball, wouldn't they always be in the same hemisphere?

I guess so too. Cause a triangular plane can be constructed with any three points in 3D space. And you can find a plane that divides the ball into two hemispheres passing through the center and parallel to the triangular plane.
_________________