Hugo is a veterinarian. He knows the following information about his 41 patrons: 20 patrons in total do not have a dog. 17 patrons in total have a cat. 7 patrons have neither a dog nor a cat. Can you help Hugo organize the results into a two-way frequency table?

Start building the two-way frequency table: it will have three rows (cat, no cat, total) and three columns (dog, no dog, total).

Start filling the table with the data you know: 
           | dog | no dog | total
cat      |        |              |   17  |
no cat |        |     7       |        | 
total    |        |     20    |   41  |

Now you can make easy calculations in order to fill the blanks:
- the number of patrons with cats but not dogs: (20 - 7) = 13;
- the number of total dogs: (41 - 20) = 21
- the total number of patrons with no cats: (41 - 17) = 24.

Now the table looks like this:
           |  dog   | no dog | total
cat      |           |      13     |   17  |
no cat |           |     7       |  24  | 
total    |   21    |     20     |   41  |

And you can use the new data to complete the table:
- the number of patrons with cats and dogs: (17 - 13) = 4
- the number of patrons with dogs and no cats: (24 - 7) = 17

The final table is in the picture attached.