Club M has 11 members and Club R has 18. If a total of 24 people belong to the two clubs, how may people belong to both?
If you had to list out all of the names of these people, there would be 11 + 18 = 29 names. Since there are only 24 people, 29 - 24 = 5 of the names must be written down twice (once for Club M and once for Club R). The answer would be 5 people belong to both.