The number of people who said they liked both cats and dogs is 39.
How to estimate the number of people who like both cats and dogs?
We shall find the number of people who liked both cats and dogs in this way:
Given:
Total number of people surveyed = 321
Number of people who like dogs = 136
Number of people who like cats = 187
Number of people who do not like cats or dogs = 41
Number of people who like both cats and dogs = Total - Number who like dogs - Number who like cats + Number of people who don't like any
Number of people who like both cats and dogs
= 321 - 136 - 187 + 41
= 321 - 323 + 41
= 39
So, 39 people like both cats and dogs.