Malaya wrote a survey question in the newspaper about changing the school colors. ninety percent of those who responded in an e-mail said they should be changed. she concludes that 90% of the student body wants the colors changed.

Her conclusion that 90% of the student body wants the colors changed is an INCORRECT conclusion. The 90% out of 100% is not referring to the total numbers of the student body.For example, 100 people are members of student body if only 50 members responded the survey, then we have:
 90% of 50 members who answered the survey said that they want the changed.