It will take 16 days for Mary to complete a certain task alone. She worked for 8 days before she was joined by her sister. both of them completed the remaining task in 2 and half days. if her sister had joined her when she started the task, how many days would it have taken?  Choices
A) 6	B) 8	C) 2	D) 5	E) 4
Explanation:   Mary and her sister complete half work in 2.5 days   =&gt; they can complete whole work in 5 days   Answer: Option 5
<result>D</result>
It will take 16 days for Mary to complete a certain task alone. She worked for 8 days before she was joined by her sister. both of them completed the remaining task in 2 and half days. if her sister had joined her when she started the task, how many days would it have taken?