Interview Case # 1 : Red clothes in Nyc
How many people wear red in New York City on a typical Monday?
Case Question :
How many people wear red in New York City on a typical Monday?
Solution
As with previous market sizing questions, the specific numbers are less important than being organized, making reasonable assumptions and being confident in your mental math.
Make sure to :
clarify the question,
break the problems into smaller pieces,
use estimation and judgement to solve each piece, and then
consolidate all of those pieces into a final conclusion.
Here is an example solution:
Ok, so here is how I would want to solve this problem. The number of people wearing red in NYC on a typical Monday will be determined by these following factors:
How many people are there in NY?
What are chances that people will wear red? This depends on two smaller factors:
How many pieces of clothes people wear
People preference in color
Now I will estimate each of those elements:
The population is about 20 million
Chances:
5% staying at home, 70% going out once, 25% going out twice
Those staying at home wear 2 pieces of clothes (pants and shirt), those going out once wear 5 pieces (shoes, pants, shirt, scarf/sweater, jacket), and those going out twice will therefore wear 10 pieces
There is no specific preference on color. I will assume that 10% of garments are red in color.
Now I will analyze the number of people wearing red at each group. I am aware that the probability calculations are not mathematically accurate, but they are good enough for a rough estimate.
1) Staying at home:
1,000,000 people
2 pieces of clothes
Chance of wearing red in each piece: 10%
1,000,000 * 2 * 10% = 200,000 people
2) Going out once: On a Monday, most will be going to work, so I will assume only a 5% chance of red for each garment:
14,000,000 * 5 * 5% = 3,500,000 people
3) Going out twice: Here the first trip is for work (5% chance) and the second trip casual (10% chance of red), i.e. 7.5% chance of red for the day:
5,000,000 * 10 * 7.5% = 3,750,000 people
So in total: there are about 7.5 million people in NYC wearing red on a typical Monday.
