Question

Jasmine is reviewing recent orders at her deli to determine which meats she should order. She found that of 1,000 orders, 550 customers ordered turkey, 305 customers ordered ham, and 225 customers ordered neither turkey nor ham. Based on these data, how many of the next 1,000 customers will order both turkey and ham?

Answer 1

Notice that 775 customers ordered turkey, ham, or both. This represents the size union of the set of customers that ordered turkey and the set that ordered ham.

Here are some helpful equations:
http://en.wikipedia.org/wiki/Cardinality#Union_and_intersection

You can apply the second one to your problem by noticing that the thing you're trying to find is the intersection of the two sets in question.