This is part of a mini-series illustrating how to think about estimation prompts for Google interviews. It is also a way to build your logic instincts.

Instructions:

1. See prompt below

2. Think about how you would estimate the answer

3. Identify the variables in your thoughts

4. Derive a simple equation

What you should avoid:

1. Overthinking

2. Trying to get it perfect

Now let’s dive in:

What is the problem:

How many iPhone and Android phones are there in the world?

What are the key elements:

• Population

• % of the population assumed to own phones

• this could be seen as % w/phones and w/o phones

What are the variables?

• X = world population

• Y = % of the population with cellphones

• Z = % of the population with iPhone & Android software

What’s the equation

(X*Y)*Z

Today we only care about coming up with an equation. If you want more on how to come up with the numbers to put in your equation, read more here.