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March 10, 2009

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(There are five practice questions in this section.)

How many weddings are performed each day in Japan?

Try a ground-up approach. In a city of 1 million (Kyoto), how many people are of marriageable age? Let's say 750,000. How many get married in a given year? Maybe 2 percent? That's 15,000. Now, the population of Japan is about 200 million, so multiply 15,000 by 200 - and you get 300,000 weddings every year. Divide that by 365 and you get 822 weddings per day (on the average, though clearly some days are more popular than others). To estimate this in your head, you could divide 300,000 by 3,000 (getting 1,000), then take off another fifth. Around 800 would be close.

To summarize:

1 million people in Kyoto

750,000 of marriageable age

2 percent get married in the average year

750,000 x 0.02 = 15,000 marriages every year in Kyoto

200 million people in Japan

200 x 15,000 = 300,000 weddings per year

300,000/365 = 822 weddings per day (or approximately 800)

How would you estimate the weight of the Chrysler building?

This is a process guesstimate - the interviewer wants to know if you know what questions to ask. First, you would find out the dimensions of the building (height, weight, depth). This will allow you to determine the volume of the building. Does it taper at the top? (Yes.) Then, you need to estimate the composition of the Chrysler building. Is it mostly steel? Concrete? How much would those components weigh per square inch? Remember the extra step - find out whether you're considering the building totally empty or with office furniture, people, etc? (If you're including the contents, you might have to add 20 percent or so to the building's weight.) ~How many children are born every day in the United States?

Population of United States: 300 million (approximately). Half are women (150 million). Perhaps half of those are of childbearing age. How do you determine how many women are pregnant at any given time? Well:

Let's say the average span of childbearing for a woman is 40 years

The average woman has two children

So a woman is pregnant one year in 20, or 5 percent of the time

3.75 million women are pregnant every year

So divide by 365 - you get about 10,000 babies a day (actually, 10,273)

Do the extra step - round up for multiple births, so maybe 12,000

How much change would you find on the floor of an average mall?

This seemingly silly guesstimate was received by a job seeker at McKinsey. It's an example of a guesstimate that is also a way to test candidate's "out-of-the-box" thinking. First, estimate how many stores there are in the average mall - say, 50. Now, how many people enter the average store on the average day? A thousand? So if there are 50,000 visitors to a mall daily, how many lose change? If one in 50, say, drops money (1,000 people a day), how much is the average loss of change? Most amounts are probably small. People carry fewer quarters, for example, and are more likely to retrieve them. So let's say that if a person is equally likely to drop a penny, nickel, or dime, then the average person who loses change loses a nickel. That means there would be \$500 worth of change on the average floor. If half of that change has been picked up immediately, that would be \$250 worth of change.

Also ask: Is there a fountain in the mall? If a fountain is considered to be the "floor" of the mall, the amount of change would obviously increase.~How many bottles of wine are consumed in the United States each week?

Determine:

1. The number of people in the United States
3. The number of wine drinkers
4. Average number of glasses of wine consumed per wee.
5. Number of glasses of wine in an average bottle

(Extra step: You may wish to estimate how much wine is used for non-drinking purposes - cooking, for example. Also clarify whether the interviewer is speaking of standard-sized bottle of wine.)

You could reasonably make the following assumptions:

• There are about 300 million people in the United States:
• Perhaps 220 million drink alcohol
• 200 million drink wine
• The average wine drinker drinks two glasses of wine a week,
• 400 million glasses of wine consumers per week
• About five glasses of wine in the average bottle
• 80 million bottles of wine consumed in America each week
• Estimate how many bottles wine is used for cooking - perhaps another 5 million
• 85 million bottles of wine consumed per week

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