I'm trying to understand the formula used to find correlation. I've far forgotten maths since I left my high school. Could, someone who've read this book, explain to me in detail, please? Below is the picture I'm wondering about..
The formula is actually pretty straight forward. Consider the table from your question.
The table states that there were a total 90 observations
Out of all 90 observations:
So we want to find out how Pizzas & Squirrels are related:
Consider the equation along with your table now,
(since squirrel is on the left)
Now that we know what these values are, let's plug them in to our formula -
correlation = (1×76 - 4×9) / √(5×85×10×80)