We can solve this problem by calculating the individual rate of working and equate it to their total rate of working.
If Dave can complete a sales route in 4 hours, then his working rate is
Also, if James can do it in 5 hours, then his working rate is
Let
be the hours that both will use to complete the sales route,
Then rate at which both completes this task is
Meaning if we add their individual rates we should get
That is;
The LCM is
So let us multiply through with the LCM.
We simplify to get,
Dividing through by 9 gives;
Therefore the two will complete sales route in
hours.
If Dave can complete a sales route in 4 hours, then his working rate is
Also, if James can do it in 5 hours, then his working rate is
Let
be the hours that both will use to complete the sales route,
Then rate at which both completes this task is
Meaning if we add their individual rates we should get
That is;
The LCM is
So let us multiply through with the LCM.
We simplify to get,
Dividing through by 9 gives;
Therefore the two will complete sales route in
hours.