A survey asked 680 runners which marathons they had run in the past year.
The results were:
340: New York marathon
400: Boston marathon
300: Steamboat Springs marathon
140: New York and Boston
90: New York and Steamboat Springs
240: Boston and Steamboat Springs
50: New York, Boston and Steamboat Springs
How many of the runners surveyed didn’t run in any of these three marathons? Note: The statistic of 340 runners who ran in the New York marathon includes everyone who ran in the New York marathon; it does not mean that there were 340 runners who ran only in the New York marathon. (This is the standard assumption in problems like this one.) The same applies to the other statistics, so the task is to deal with the overlap. (This explains, for example, why the numbers in the whole list add up to more than 680.)
Draw a Venn diagram
Here is my quick sketch Venn diagram..... add up all of the numbers then subtract from 680 to find runners who participated in none...