其它
Chloe and Zoe are both students in Ms. Demeanor\textquotesingle s math class. Last night they each solved half of the problems in their homework assignment alone and then solved the other half together. Chloe had correct answers to $80\textbackslash\%$ of the problems she solved alone, but overall $90\textbackslash\%$ of her answers were correct. Zoe had correct answers to $75\textbackslash\%$ of the problems she solved alone. What was Zoe\textquotesingle s overall percentage of correct answers? (adapted from 2017 AMC 8, Question \#14) 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Percentages Word Problems
Assume the total amount of problems is 100 per half homework assignment, since we are dealing with percentages, and not values.  Then, we know that Chloe got 80 problems correct by herself, and got 180 problems correct overall.  We also know that Zoe had 75 problems she did correct alone.  We can see that the total amount of correct problems Chloe and Zoe did was $180-80=100$. Therefore Zoe has $100+75=175$ problems out of $200$ problems correct. Thus $\frac{175}{200} = 87.5$ percent. 