To finish a certain work, it will take 12 days by Taro and 15 days by Jiro.
Taro and Jiro jointly started to finish the work but Jiro rested a number of days.
It took 8 days to finish the work.
How many days did Jiro rest ?
Answer
3 days
Solution
The volume of this work is set to 1.
The daily work load of Taro is 1/12 and Jiro is 1/15.
For two persons, total daily work load is 1/12 + 1/15 = 3/20.
Since the work load at the time of working for eight days by two persons is set to 3 / 20 × eight-day =6/5.
The difference between 1 and 6/5 comes to the work load Jiro rested.
It is (1/5)/(1/15) = 3 days that Jiro rested.