Ryan answered $$(0.8)(25)=20$$ problems correct on the first test, $$(0.9)(40)=36$$ on the second, and $$(0.7)(10)=7$$ on the third. This amounts to a total of $$ 20+36+7=63$$ problems correct. The, total number of problems is $$25+40+10=75$$.Therefore, the percendage is $$\frac {63}{75}\to(\rm D)84$$. 
Kevin got $$80\textbackslash\%$$ of the problems correct on a $$25-$$problem test, $$ 90\textbackslash\%$$ on a $$40-$$problem test, and $$70\textbackslash\%$$ on a $$10-$$problem test. What percent of all the problems did Kevin answer correctly? (2010 AMC8 Problem, Question \#9) 

1) $$64$$ 
2) $$75$$ 
3) $$80$$ 
4) $$84$$ 
5) $$86$$ 