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A.5. Brain teasers

A.5.1. Estimation

What’s an estimate for how many mini shampoo bottles are used by all the hotels in the United States in a year?

Example answer

I estimate the number of bottles by using the following formula:

number of hotels in the US * average number of rooms per hotel * 1 shampoo
bottle per occupied room per night * average room utilization * 365 days per
year = number of shampoo bottles per year

Then I estimate the numbers in the formula:

• Number of hotels in the United States— If I assume that there is a hotel for every 5,000 people in the country, and there are around 300 million people in the country, that’s 60,000 hotels.
• Number of rooms per hotel— Fifty seems like a decent guess for the average number of rooms ...