A survey was made of 200 students to study their use of the public library system. The findings were as follows:

Question

60 used the Reader’s Guide.
28 used both the card catalog and the information booth.
68 used the information booth.
83 did not use the library.
43 used only the card catalog

Explain how the above information can be used to conclude that some students must use both the information booth and the Reader’s Guide.

Answer 1

200 - 83 = 117 use the library

60 + 28 + 68 = ?

Answer 2

156