word problems

[Guest]

In a survey, the respondents asked two questions. In the first question, 85% of respondents answered correctly, while the second question answered 75% of the respondents correctly, while 120 respondents responded correctly in the two questions asked. If each respondent answered at least one question, then how many people responded correctly only to the first question?

[Monox D. I-Fly]

I got [tex]\frac{120}{100%-85%}\times85%=\frac{120}{15%}\times85%=8\times85=680[/tex].