Question

a woman can do a certain job in 10 hours and her younger daughter can do it in 12 hours. after the woman and her younger daughter have been working for 1 hour, they are join by the older daughter and the three complete the job in 3 more hours. how will it take the older daughter to do the jib by herself. please help i'm really confused.

Answer 1

Let'a divide the job into 60 parts (LCM of 10 and 12).
The woman can do 6 parts an hour.
The younger daughter can do 5 parts an hour.
Together, they do 11 parts an hour. 49 parts left when the older daughter joins.
Let the older daughter's work speed be Y.
So 3*(11+Y)=49
33+3Y=49
3Y=49-33
3Y=16
The older daughter does 5 and a third parts an hour.
So 60/5.333...=11.25 hours

Answer 2

thank you!