其它
Alicia, Bryant, and Charles work for a software company and they want to write a particular computer program. Alicia and Bryant first write $\frac{1}{3}$ of the program in $6$ days. Then Bryant and Charles write $\frac{1}{4}$ of the remaining program in $2$ days. In the end three of them work together to finish the program in $5$ days. How many days will it take if Alicia works on the program by herself? 
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In the second part, Bryant and Charles can write $\left( 1-\frac{1}{3} \right) \times \frac{1}{4}=\frac{1}{6}$ of the program in 2 days. Therefore, they can write $\frac{1}{6} \div 2 =\frac{1}{12}$ in one day. There is still $1-\frac{1}{3}-\frac{1}{6}=\frac{1}{2}$ left.  Now in the last part, they work together and finish in $5$ days. They can write $\frac{1}{2} \div 5=\frac{1}{10}$ in one day. Therefore, Alicia can write $\frac{1}{10}-\frac{1}{12}=\frac{1}{60}$ in one day, which means she needs $60$ days to complete. 