At my office, 16 people own cats, 9 people own dogs, and 5 people own both cats and dogs. How many people own a cat or a dog?
(Remember that in mathematics, the word "or" is used in the inclusive sense. So if you own both a cat and a dog, then you are included in the category of people "who own a cat or a dog".)
+79 so we have 17-3+9-3=14+6=20 so 30 people own a cat or a dog
Alternate way:
there is 17+9-3=23 people we then do 23-3=20 people who own a cat or a dog
