2. the number of people at the sale was 210 to start off with. when you arrived if 50% of the people left. how many people were left?

Well, we know that 50% of people left. Since there can be no greater than 100%, we know that stayed.

Now, we need to figure out what 50% of 210 is. To do this, we can convert 50% into a fraction:

Now, let's multiply this fraction by 210 to find a number of people. This would be:

Our answer is 105 people.