OpenStudy (anonymous):

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?

OpenStudy (anonymous):

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.