Question 285536
r/x+r/2x=1
2r+r=2x
3r=2x
r=2x/3
in one day they can do 3/(2x)
It takes them r days working together.

3r/2=x 
3r=2x
if x=5
r/5+r/10=1
2r+r=10
3r=10
r=10/3 =3 1/3 days
if one can do it in 5 days the other in 10 days together they can do it in 3 1/3 days

in one day one does 1/5 and the other 1/10

2/10+1/10 they can  do 3/10 in one day working together.