Answer :
This can be treated as a work problem and we can solve it as follows:
Harland working alone = 15 minutes
Trudy scatters the leaves + Harland rakes = 20 minutes
We set scattering as a negative value.
1/15 - 1/x = 1/20
x = 60 minutes for Trudy to scatter the leaves alone
Harland working alone = 15 minutes
Trudy scatters the leaves + Harland rakes = 20 minutes
We set scattering as a negative value.
1/15 - 1/x = 1/20
x = 60 minutes for Trudy to scatter the leaves alone