Answer: If T is the time you wait to trim the lawn since you last did it and B is the lenght at which you trim, then the speed will be:
[tex]v=\frac{B}{T}[/tex]
Explanation:
Let's say T is the time you wait to trim the lawn since you last did it (1 month for example) and B is the lenght at which you trim (10cm for example).
If v is the speed at which the lawn grows, then the lenght of the lawn as a function of time will be:
[tex]b(t)=b_{0}+ vt[/tex]
where [tex]b_{0}[/tex] is an arbitrary initial lenght. Let's say [tex]b_{0}=0[/tex].
[tex]b(t)=vt[/tex]
Then we have:
[tex]v=\frac{b(t)}{t}[/tex]
So, at time T the lawn has grown a lenght B. And the speed is:
[tex]v=\frac{B}{T}[/tex]
