Elizabeth can get a certain job done in 15 days, and Tony can finish only 75% of that job within the same time. Tony worked alone for several days and then Elizabeth joined him, so they finished the rest of the job in 6 days, working together.
For how many days have each of them worked and what percentage of the job have each of them completed? Choose the correct choice:
A) 5 days and 40%  B) 6 days and 30%  C) 6 days and 40%  D) 7 days and 40%  E) 7 days and 30%
First we will find the daily productivity of every worker. If we consider the whole job as unit (1), Elizabeth does 115 of the job per day and Tony does 75% of 115, i.e.   75100⋅115=120. Suppose that Tony worked alone for x days. Then he finished x20 of the total job alone. Working together for 6 days, the two workers finished 6⋅(115+120)=6⋅760=710 of the job.   The sum of x20 and 710 gives us the whole job, i.e. 1. So we get the equation:   x20+710=1   x20=310   x=6. Tony worked for   6 + 6= 
<gadget id="calculator">  6 + 6</gadget>
<output>12</output>
12 days and Elizabeth worked for 6 days. The part of job done is 12⋅120=60100=60% for Tony, and 6⋅115=40100=40% for Elizabeth.   Answer is 6 days and 40%.
<result>C</result>
Elizabeth can get a certain job done in 15 days, and Tony can finish only 75% of that job within the same time. Tony worked alone for several days and then Elizabeth joined him, so they finished the rest of the job in 6 days, working together.
For how many days have each of them worked and what percentage of the job have each of them completed?