Consulting 7.3 Dealing with numbers: Guesstimates and brainstorming

This lesson will help you brainstorm and estimate data, percentages and trends. 


The previous lessons were about a wide variety of ways of describing data. This lesson will build on that language and help you use it to discuss and estimate big-picture ideas. 

Warm Up: 

Guesstimates are a common aspect of the hiring process at many consulting firms. Have you done this before? Do you do it now?


A. Clarifying is important. Look at the following examples: 

Question: How many people in your city do you think are wearing red today?

  • How do you define “red”?
  • Does that include all shades? 
  • Burgundy wouldn't be considered red, would it? 

Now, use similar questions to define the question, "How many people will take public transportation in London on a typical Monday?"

B. When brainstorming, you may want to use vague language. Look at the following words or phrases, discuss anything new with your instructor, and practice using each one:

  1. A back-of-the-envelope calculation 
  2. A ballpark figure/in the ballpark of 
  3. In the neighborhood of 
  4. In the region of
  5. In the vicinity of 
  6. Approximately 
  7. Roughly 

C. After clarifying, typically follow these steps. 

  1. First, break the problem into smaller pieces. You might try to be MECE (mutually exclusive, collectively exhaustive).
  2. Then use estimation and judgment to solve each piece.
  3. Finally, consolidate all of those pieces into a final conclusion.

Let's practice a few guesstimate questions: 

  1. How many dogs are there in New York City?

  2. How many people in Tokyo will buy iced tea from a vending machine today? 
  3. How much money do people in your country spend on chocolate in an average month?