Answer:
It would take 120 minutes to mow the lawn by herself.
Step-by-step explanation:
The person's rate is [tex]\frac{1 lawn}{24 minutes} =\frac{1}{24}\frac{lawn}{minute}[/tex].
The dauther's rate is [tex]\frac{1 lawn}{t}[/tex].
The combined rate is [tex]\frac{1lawn}{20minutes}[/tex].
So, as this the same lawn if we use the formula for combined rates we can get the answer
Person's Rate × Combined time + Daugther's Rate × Combined time =1
[tex]\frac{1}{24}20minutes+\frac{1}{t} 20minutes=1[/tex]
We have to multiply all the equation by 24t:
20t+480=24t
t=120 minutes
