Algebra. Please help?

Question

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

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

83 of the 200 surveyed didn't use the library at all, leaving 117 (200 - 83) who did. All of the other folks are library users.

68 of those 117 used the information booth, leaving 49 (117 - 68) who used the library BUT NOT the information booth.

Since 60 used the reader's guide, and at most 49 library users didn't use the information booth, a minimum of 11 (60 - 49) reader's guide users must have also been information booth users.

Answer 2

I honestly have no idea, but I would try and play around with the numbers.